Well, there are some things from the Bantam Spectra books that give hints at when it was:
- In the Thrawn Trilogy, it mentions some Bpfasshi Jedi went rogue during the Clone Wars and were hunted by Yoda about 30-35 years before the book (20-25 BBY). Also, it says the Battle of Honoghr from the Clone Wars dates back to 35 BBY.
- In Darksaber of the Callista trilogy, it states that the former Jedi Callista knew Obi-Wan as she refers to him as General Kenobi.
- In I, Jedi, we're told by Hal Horn's recording that his father, the Jedi Nejaa Halcyon, fought in the Clone Wars and died shortly after, when Hal was ten. This could put the Clone Wars sometime close to 30 BBY as Hal's son, the famous X-Wing pilot and later Jedi Knight Corran Horn, was born around the same time as Luke.