I still think 1 hour/level is a silly duration. At 13th level (the soonest you could cast it) it would last 13 hours (or more than 1/2 a day) at 20th level (highest level supported by core rules) it would last 20 hours (or almost 1 day). In the 7 levels since you could cast the spell you have not even doubled the duration. Compare this to Mage Armor (only other 1 hour/level spell I can think of off the top of my head) and its constantly improving itself. Hence, I think the duration should be a flat "up to 24 hours (D)".
Technik
Technik