Updated - Mar '12
A long time ago, a thread was made concerning the voyage length of One Piece, and it turns out that most people paid little attention to that aspect of OP. In fact, Oda is so godly in his story telling that most people had their own theories on the voyage length, yet there was no canon evidence for those theories. In case anyone missed the original thread, HERE IT IS. I'm adapting Roman Zaenom's excellent post and format, since he went through all the trouble of reading through all those chapters (everyone was too lazy to do it). I've included more chapter info on all of RZ's stuff as well as some of my own findings.
EDIT (Mar 12): Most recently, FrankyFan has added his work to ours. I've got a life and career to pursue nowadays, so updates will be rare (but of course I'm still reading OP). Like FrankyFan, feel free to add your finding to this thread! I will update it whenever I can.
The "Time/Event Map" will be divided into 4 parts:
PART 1: Little Garden to Skypiea
PART 2: Long Ring Long to Water 7
PART 3: Thriller Bark to Red Line
PART 4: Shabondy to Marineford
Everything before & between these sections CANNOT be confirmed, and therefore relies on pure speculation.
PART 1: FROM LITTLE GARDEN TO SKYPIEA
DAY 1 (Ch 115-129)
SH meet Dorry and Brogy, fight Mr.3, Nami is stung by a 'Keschia' bug
DAY 2 (ch 130-131)
SH meet Wapol
(ch130 p.18 : says that one day has passed)
DAY 3 (Ch132-154)
Arrival at Drum, SH meet Chopper and leave Drum the same night
(ch132 p.03 : Usopp asks about Wapol that they met the day before)
(ch135 p.13 : Chess confirms on Drum they saw the SH the day before)
(ch139 p.12 : Kureha says it's the third day of incubation of Nami's virus)
(ch152 p.17: Chopper agrees to go with them)
(ch154 p.10: they leave at night with a full moon)
DAY 8 (ch156)
SH meet Mr.2
(ch156 p.01 : it's been 5 days since they left Drum)
DAY 12 (ch157-164)
SH arrive at Alabasta, visit Nanohana and sleep at Yuba. BW gather at Spider's Cafe.
(ch157 p.02 : Zoro says they haven't eaten for 4 days. We know they already didn't have food when they met Mr.2, 5 days after they left Drum. So, Day12 is the latest time they could have reached Alabasta)
(ch160 p.05 : BW is said to meet at 20pm the same day at Spider's Cafe)
(ch 161 p.04 : The SH reach Elumalu hours before BW gather at SC)
(ch 161 p.05 : Vivi says there's still half a day before they reach Yuba)
DAY 13 (ch165-167)
Baroque Works gather at Rain Base, SH in the desert
(ch160 p.05 and ch165 p.15 : on day 12, Crocodile said the Utopia Mission would start "the day after tomorrow at 7am" and here tells BW it will happen "tomorrow at 7am", which means it is day 13 when BW meet Crocodile)
(ch167 p.18 : when the SH are in the desert, there's 17 hours left before Utopia, which means it's 1pm)
DAY 14 (ch168-212)
Day of the Rebellion, BW defeated
(ch168 p.01 : the sun sets then rises again)
07:00am (ch170 p.18 : Utopia Mission begins)
10:00am (ch180 p.08 : storm in Yuba, 5h left before rebels reach Alubarna)
11:00am (ch180 p.10 : SH cross river Sandora with crab, 4h left)
12:00pm (ch180 p.15 : Karue and ducks join the SH, 3h left)
15:00pm (ch173 p.01 : Crocodile said at 7am the rebels would reach Alabasta in 8 hours : 15pm)
16:30pm (ch207 p.15: see the clock when the bomb explodes)
DAY 17 (ch213-214)
Luffy wakes up, they party and leave at midnight exactly
(ch213 p.8 : Luffy slept for 3 days and missed 15 meals)
(ch214 p.13 : Nami tells Vivi they'll meet at 12pm the next day in 12h, so it's midnight when the SH leave Alubarna)
Ace joins Buggy. Shichibukai gather at Marie-Joa. SH leave Alabasta at 12pm, Robin joins immediately after, a ship falls from the sky a few minutes after that and they meet Masira the same day. Then they go to Jaya and meet Bellamy. At night, Luffy defeats Bellamy.
(ch229 p.10 & 13 : Cricket says that when it becomes dark in Masira's territory, the knock-up stream happens the day after, so we know the SH are on Jaya the same day they met Masira - yes, the same day they left Alabasta!)
(ch233 p.08 : The day before Bellamy gets beaten, we see Ace join Buggy's crew and the meeting at Marie-Joa, then we go back to Jaya at night where Blackbeard beats Sarquiss and leaves Jaya to capture Luffy)
***CONTROVERSY*** This is where a lot of controversy lies.... Roman Zaenom thinks they meet Masira's crew ON THE SAME DAY that Robin joins the crew since there is no properly labeled time skip. However on Chap218, page 8 we seen the crew still wearing desert clothing, and in following pages, they appear to have changed. Some members think this is a stylistic indication of a mini time skip, and if that were true, I'd say it was no more than a day because they are still getting to know Robin (e.g. Usopp interviews Robin in his normal clothes). To be honest, I'd like to think there is more time between Alabasta and Jaya as well, but I will continue with Roman Zaenom's count until Oda himself reveals more about the timeline.
DAY 19 (ch235-254)
Knock-Up stream, SH in Skypiea, Satori's trial of orbs, Party at night
(ch235 p.13 : knock-up stream at 10:00am)
DAY 20 (ch255-301)
Survival, Luffy defeats Eneru, Party the same night
(ch254 p.12 : Eneru says on day 19 the Shandia will attack again the day after)
(ch300 p.12 and 15-16 : Night time already, party)
SKYPIEA AFTERMATH/PARTY: + several days
(ch301 p.1: The celebration lasts for + several days)
NOTE: We have no idea how long they partied, but Roman Zeanom points out that "they get attacked by Sea Monkeys the moment they land on sea. Those same three Sea Monkeys sunk the Frog Captain's boat right before they reach Long Ring Long Land. So, they're not too far away." It is unfortunate, but it may be deduced that the crew finds LRL immediately after they get off Skypiea thus reducing the amount of days travel In case anyone is interested, everything from the beginning of the Grandline to the end of Sky Piea is 21 Volumes.
PART 2: LONG RING LONG TO WATER 7 & ENIES LOBBY:
DAY 1 (ch304-321)
Land on LRL. Meet Tonjit. Davy Back Fight. Fight Ao Kiji
DAY 8 (ch322-333)
Meet Kokoro @lighthouse. Land on W7 shortly after. Robbed by Franky Family; Usopp vs Luffy fight, Iceburg shot
(Ch322 p.1: they spent another 4 days moored on LRL, and sailed for 2 days more days. On the third day, they hit Kokoro's lighthouse.)
(ch332 p.3 & 4: Usopp sets the duel at 10pm, and Sanji accuses Zoro for not 'finishing off' the franky family when they came during the [same] day)
DAY 9 (ch334-365)
Franky comes back, and fights with Luffy and Shipwrights. SH and CP9 infiltrates/attacks Gallera at night. Franky's flashback. Aqua Laguna hits right after CP9 leaves :
(ch334 p. 4: Morning after Usopp vs Luffy fight)
(ch335 p. 9: Aqua Laguna announce to arrive around midnight)
(ch364 p. 13: Paulie tells the crew that the Aqua Laguna would last only the night, and it would be safe to sail in the morning after)
10:30pm (ch360 p. 8: Nami & Paulie heads to station)
11:00pm (ch361 p. 16: Sanji boards train)
(ch363 p. 12-13: Aqua Lauguna hits)
DAY 10 (ch366-430)
Assuming the day starts at midnight, Rocket Man heads out. Raid on Enies Lobby begins in the middle of the night, and ends some time in daytime. Merry gets sent off.
(ch377 p.9, 16-17: Spandam commands everyone to wake up, but the guard says it's still night. O & K wants to finish the intruders quickly and go back to sleep. So it can't be 6 or 7am yet)
(ch430: It's daytime on the sea between EL and W7 when we run into the Gallera ship. Iceburg's flashback shows the Merry heading off during the Aqua Laguna.)
Merry gets to EL just in time to rescue them, meaning the time it takes to sail through the AL must be equivalent to the lenth of the Raid on EL. I assume Iceburg and the Gallera ship departs W7 asap, meaning the morning/night after the Aqua Laguna subsides. So unless it takes MORE THAN 24 hours to sail from W7 to EL under normal conditions, Merry's 'sending off' must take place on the afternoon/morning of DAY 10.
DAY 12 (ch431-433)
Garp, Coby, Helmeppo shows. Party for the rest of the day. Whitebeard and Shanks meet. Ace vs Blackbeard fight
(ch431 p. 3: "2 days after the incident")
(ch323 p. 1: Kokoro said it takes around one week for the log post to set)
(ch431 p. 10: Kokoro says they have a "couple days" till the log sets in my scan, but in Stephen's page, it says "2-3 days.")
It's later confirmed that their log sets 3 days later. Hence, it's only been 4 days since they landed on W7.
(ch433 p.15: After Coby and Helmeppo leaves, they have a big party, and you can clearly see the sky getting dark. The sunset is shown way better in the Anime eps 315.)
Construction on Thousand Sunny begins. Usopp rehurses his 'return speech'
(ch435 p.7: it takes 5 days to construct Thousand Sunny.)
(ch435 p.9: Sunset shot proves that Franky and the shipwrights start contruction on the day after the party.)
New Bounties come out. Thousand Sunny completed. Usopp rejoins. Departure from W7.
(ch435 p. 10: Their log sets on the third day of the wait.)
(ch440 p. 11: Ace and Blackbeard fight 3 days before everyone gets finds out about the SH bounties.)
(ch435 p. 14: Ship completed 2 days ahend of schedule because the shipwrights worked day and night to finish it)
Sailing time between Water-7 and Florian Triangle is UNKNOWN. Ch440 and 441 is the Bounties chapter and the Ace vs BB chapter so it only took 15 days in OP time for for 131 chapters (ch304 to ch435) to transpire. That's 13 Volumes!!!
PART 3: Thriller Bark to the RED LINE
DAY 1 (Ch442-482)
Arrival to Florian Triangle. Meeting with Brook. Captured by Thriller Bark, and just about all fights until the sunrises the next day.
Instead of counting DAY 2 from midnight (like b4) I'll count it from first light of dawn because there is no way of telling what time it is on TB.
DAY 2 (ch483-486)
Kuma vs all. Kuma leaves. Conclusion of the fight. News is out on Ace's defeat and Blackbeard's new status
(ch483-485 is basically the entire duration of the sunrise.)
DAY 3 (ch486-489)
It's a celebration bitch!! Brook's flashback. Brook joins
(ch486 p. 4: One day after Moria's defeat.)
DAY 5 (ch489-490)
Departure from TB. SH finds out about Ace's diminishing Vivrecard/lifeforce. Kuma and Garp piss Sengoku off
(ch489 p. 11: 2 days after Brook joins.)
Sail to the Red Line + Several days (ch490)
Hit the Redline. Meet Caimie and Pappag
(ch490 p.9: a few days after leaving TB, they finally get there!!!!!)
PART 4: Shabondy to Marineford
A) Twin Cape and Little Garden
B) Sky Piea and Long Ring Long
C) Water 7 and Thriller Bark
D) Thriller Bark and the Red Line
Now, if we estimate the times of A-D to be around 2-3 weeks, then the voyage length of One Piece from the beginning of GL to the day of Ace's execution on Marineford (chap 101 to 580) would be around 72 days. That's less than 3 months!