In the Beginning: 10 years before season 1 starts.
The Gathering: Approximately 6 months before season 1 starts.
Thirdspace: Season 4, between the First Ones leaving for the Rim, and Sheridan's war against Earth.
River of Souls: One year after Season 5.
Crusade: 5 years after season 5.
Legend of the Rangers: Not sure, but roughly 20-odd years after season 5.
I pretty much agree with everything everyone else has said since Eryx posted this except a couple of minor things.
River of Souls happens 6 months after the end of Season 5 (About June July 2263). We know this because Lochley mentions to Garibaldi it has been 6 months since he left (At the end of season 5/end of 2262)
Thirdspace happens sometime in the latter half of Season 4 (2261). I worked this out once but can't quite remember the 2 episode timeframe I worked out. You have the fact that Zack has his new uniform in Thirdspace so it must be after the "Next time use a bigger needle" scene where he is being fitted for it. Also Delenn and John are both on the station which narrows it down to times when that could happen, i.e. before Sheridan goes off to fight the Civil War, and sometime when Delenn isn't offing kicking Drakh behind or solving the Minbari civil war. Also, since Garibaldi isn't in the movie we can probably assume it is sometime after he has gone to Mars to work for Edgars. Just in case anyone wants to try and recreate my reasoning for themselves. (Having read what I looked up later I peg it as sometime between the end of 4.14 "Moments Of Transition" and the start of 4.17 "The Face of The Enemy" Though I could be wrong, but I'm sure I'm close 8) )
Crusade. Well Call to Arms is supposed ot be on the 5th anniversary of the formation of the ISA so that would placve it End 2266/Start 2267, Crusade follows directly on from there.
All of the above is from memory. Now to go and look up my vast array of B5 sources of info, feel free to talk amongst yourselves for a bit . . . . . .
(Returns from behind a pile of magazines)
The following is info from the Official B5 Timeline as made by a fan (not me!), sanctioned by JMS and then printed in the official B5 magazine.
In The Beginning
The Minbari War is listed as having taken place between July 2245 and 2248. A Late Delivery From Avalon (Season 3 July 2260) is cited as the 15th anniversary of "The Prometheus Incident" which confirms this.
The Gathering Sun 3rd January to Fri 8th January 2257
(Also states Sinclair took command of B5 Monday 9th March 2256)
Thirdspace is tagged as June 2261, after Delen has returned and recovered from her injuries in the Starfire wheel. Thirdspace happens after this and before Delenn is recalled to Minbar. the best it ties it down is after Ep 4.14 "Moments of Transition".
River Of Souls Tuesday 8 to Sunday 13th June 2263. Bryson arrives on station 11th June.
Call to Arms/Crusade. Call to Arms is Tuesday 17th to Monday 30th December 2266. The attack on Earth happens on the 28th December.. Episode 1 of Crusade "War Zone" happens Wednesday 1st to Sunday 5th January.
As I've often said, and most of my friends agree, what little info about B5 I can't remember off the top of my head, I know which of my vast array of books, etc. to look it up in
Lastbesthope (For B5 info)