Board Thread:Game Discussion/@comment-33232140-20171002045207/@comment-30967537-20171002072951

Tommy is correct on both counts ... They're both 7-day events so, if you can't start them before October 16th, just to be sure, maybe you should pick the car you definitely want to win ... good luck.
 * You can finish one Flashback challenge and start another on the same day, the only restriction is that you can't have two open at the same time.
 * Unless FM push the closure of a Flashback challenge (which they probably could do but haven't yet done) and as long as you don't update the game before completing all of the Flashback challenges you want to do, then you should be ok.