Anijen compiled
this masterpiece a while back, and I've taken it as my canon ever since, so that's a good place to start.
I've never seen a very specific timeline for the series proper, but if you're going by Anijen's timeline and the information we're given in
The Beginning, the war must have ended before the release of the final book. That is, the series started in 1996, and we're told in #54 that it's taken about three years, which would put the end date somewhere in 1999 or early 2000.
There's a jump of "one year later" in #54 that can then fall somewhere in 2000 or early 2001, but May (the publication month of #54) might be pushing it. Depending on how loose you want to get with your times there and how strictly you want to stick to that timeline, of course. Since May 2001 can be made to fall awfully close to the events actually taking place in #54, you probably can't go wrong by setting it as the date of either
[spoiler]The stealing of the Yeerk ship or the encounter with The One.[/spoiler]
*shrug* Might be helpful info, should you choose to use it.