as much as three hours还是as many as three hours?

同意三楼的。

时间是论长短不论多少的，虽然汉语也可能会说多达几个小时，可是一般可没人那么说，都是说长达吧

但是如果非用MUCH和MANY来形容的话，用MUCH。不是因为单数复数，而是MUCH是固定用语

用much.
因为当一个复数名词表示时间的时候，它用作不可数名词。比如Three hours is a long period.

都不对!

应该是: as long as 3 hours.

as many as three hours

恩～
第三种读起来比较顺口．

as much as