Timeframe: I hope it's in either modern times or the 80s...I didn't really like the 90s theme of SA. I believe it will be present day theme b/c when the games are GTA 1/2/3 they are present day games. When the games had the name of the location in it they took place in a different era.
The location: Hopefully they'll include all the previous cities, with additions onto Liberty City and Vice City. Also I hope they'll introduce a whole new city. Someone mentioned the idea of being located in South America with drug cartels controlling everything. I think it would be really cool to introduce a small island system off the coast of Vice City...I guess they would basically be the Bahamas. This could be a place that is controlled by drug cartels and give you that lawless South American feel with that classic North American location.