I am not sure, but i did find a video about it on their site.
Timeline Video
I did also find this in the FAQ on their site.
Q:When does Star Wars: The Old Republic take place in relation to the movies?
A: Star Wars: The Old Republic takes place more than 3,500 years before the rise of Darth Vader. The most powerful Sith Empire in history has emerged from deep space to attack the Republic and its legendary Jedi guardians. After decades of war, a tenuous truce has been established between the Sith Empire and the Republic, but events occurring in the game are leading the galaxy back to an all-out war.
If all above fails, i hope this link will help you understand the timeline:
http://en.wikipedia.org/wiki/ChronologyofStar_Wars
Tried to dig a little in the rp forums of SWTOR, and found out many people used BBY as their date of birth, so i searched google about BBY and found that link.
Hope it helps.
Snow.
