IPSec like strongSwan can be configured to do rekeying after time or bytes transferred or packets transmitted. Is there any recommendations to set those settings? Maybe according to algorithms used?
This isn't specific to StrongSwan, but here is a Cisco article relating to rekeying. In this example, keys are replaced every 1,000 or 10,000 seconds. It is, obviously, best to rekey as often as possible, while taking into consideration hardware limitations. I would say that every few hours would be more than enough.
-Hope this helps.