An hour is, in real life, 60 minutes or 600 rounds.

Usally in a module, like the Official Campaign, the amount of minutes in an hour is drastically lowered to allow quicker passage of time. A usual value is 4 minutes per hour (thus it is 40 turns for an hour), but this heavily varies from mod to mod. The range can be anywhere from 1 minute / hour to 60 minutes / hour. The NWN2 Official Campaign scales 2 minutes / hour.

Some longer lasting spells are timed in hours rather than minutes or rounds.

Resting in NWN2 assumes 24 hours has passed (which is hardcoded), therefore most spells end when finishing resting unless they last over 24 hours. Persistant spell effects cause spells to last 24 hours. Thus, they fade upon resting. As such, with the addition of the MotB expansion, high level characters would actually be better of NOT persisting spells that last 1 hour / level.