We recommend that you use a 3+1 interval timeout. Keep in mind, we keep sending monitors even when the system is down. A five minute interval is extremely long, but might make sense in your situation. Our default is a five second interval with a sixteen second timeout. In that situation (taking a simple SYN monitor), we would work as follows:
0 sec - SYN
5 sec - SYN
10 sec - SYN
15 sec - SYN
16 sec - we would mark the pool member down here
20 sec - SYN
25 sec - SYN
30 sec - SYN
SYN/ACK
ACK - we would mark the pool member up here, unless told otherwise by the config.
If you had an HTTP monitor, there would just be more traffic, and with a 5 minute interval and sixteen minute timeout, we would send a monitor every five minutes and mark the pool member down after sixteen minutes of no response. You would still have only four monitor outstanding, however.