Because its not straight PnP DND. NWN couldnt let you run around with all those spells on for an hour per level, aat level 18 you could rub around with Stone skin or GMW on longer then you'd even want to play the game...PS - In Game Hours are like Turns. (Ever notice the compass in game keeps track of time In World?) Another reason
While you are right, Stone skin is 1 hour/level hehe.
Turn/level = minute/level in RL terms while hour/level = 4 minutes/level in RL terms. This means that the duration is a lot lower but still reasonable compared to the rest timer that also scales with level although not excatly as 1min/level but in a bit more advanced way but this makes it so that you actually gain something as you level up in wizard duration wise since you with the hour/level would have a quite decent duration already at level 4-5 while you now gain something as you go up since you normally rest around every 10-20 minutes when you are out adventuring ((Not including RP time and extremly long rest timers here)) depending on level and how much you are dependant on mage levels. So having the system this way makes the progression more attractive as in duration increase compared to D&D, plus I guess the biggest reason is that it is nwn stardart anyway so it simply carries over from there... But at least that are the two reasons I think there are for it, some might know more...
I thought an ingame hour was two turns, a turn one minutes, so an hour is two minutes.Which makes an ingame day a total of 48 RL minutes.
May have to get a correction on this, but the 1/hour per level = 10 RealLife/level.
LORE: RoundA IG day is 96min. 1hour IG = 4min RL/4turns>Xirion>
I suppose it'd make more sense if you can rest in dungeons ... can you?-Lydyn
P.S. - 'Course, mages are always at a disadvantage in no rest areas, especially with a system like this because unless they're pure, their spells run out so fast ... or even depending on the dungeon, unless the mage is epic, their spells will poof before they can transverse the entire dungeon.
Now I only wonder why IG time moves so darn fast ... *Shrug*-Lydyn