I'm peering with my isp, and they're advertising my block. I have two sites that they'll be peering with. If my main site goes down (for a LONG time like 4 - 6hrs.), I want the block to roll over to the other site. The problem is I don't know of a way to make bgp wait that long. Is this type of scenario one that will require me to call the provider and then have them manually peer the other site when it's a true disaster? I don't want bgp to failover after a minute of disconnection with my main site.
Talk to your provider and see if you can come up with some appropriate neighbor timers on your peering to the main site.
Timers can be configured at the neighbor level so the provider won't affect other peering within their BGP process, sames goes for your config.