Just finished reading this whole thread, and I thought I'd through my two cents worth in.
Seems everyone missed this comment by TrueCreation
1. What time period are we talking?
If you mean to imply what geologic time period like triassic, jurrasic, etc then I would have to say every time period, but If you are just asking how long ago it happend then I would have to say about 4,500 years ago.
Now as an Archaeology student, I find this strange considering 2500 BCE is smack dab in the middle of the Old Kingdom in Egypt and the Early Dynastic II period in Sumeria. I would love to know during the reign of which the Flood happened. pharoahhttp://touregypt.net/kings.htm
(Hint: there are still records from the 1st and 2nd Intermediate periods, so don't go choosing that one to quickly)