How to add delay when activating a pool member

The best place for a requirement like that is in iControl. A possible iRule solution could be handled by measuring the time of failure on server one, then checking to make sure 5 minutes has passed, then up server two and reset the failure variable back to 0. You need to be on a 9.2 version, and someone else might post back on a better event to place the checking other than CLIENT_DATA. I usually only use the HTTP events, so I'm unclear what's best for not HTTP traffic.

when CLIENT_CONNECTED {
  set failure 0
  set time_failed 0
}
when CLIENT_DATA {
  if { $failure } {
    if { [clock seconds] > [expr { $time_failed + 300 }] } {
       LB::up pool yourPool member 2ndServer yourPort
       set failure 0
    }
  }
}
when LB_FAILED {
  set failure 1
  LB::down pool yourPool member [LB::server addr] yourPort
  set time_failed [clock seconds]
}

This is untested! It might not work, but maybe it will get the wheels turning for you...