Fikealox:I always thought that the 'imbue item' spell has to be indefinite (that is, if you want a magical item that wont expire), but that the other spell only has to be indefinite if it's an 'always on' effect.
A: Only the Imbue Item spell needs to indefinite, unless one of the imbued spells has a permanent effect, in which case it also needs to be indefinite. It the spell just has a triggered activation, it needs to last only as long as you want it to (by choosing its Duration factors during the Imbue Item casting).