Values in scripts don't have units - how they should be interpreted depends entirely on how they are used.
I haven't been able to find any reference to a "SetEncounterZone" command. Is that a script function you're talking about?
Cipscis
Sorry, I worded it wrong. It's actually SetZoneRespawns:
http://geck.gamesas.com/index.php/SetZoneRespawns
So it should be possible to set up a random value for that to occur if I can figure out how to get the game to recognize a time value. I've come across the Globals that deal with time, like GameDaysPassed etc. but those don't strike me as anything I can use in this context. I'd like to have something like iHoursToRespawnCell * GetRandomPercent, but I'm not sure how to make it work.