You CAN use it from invintory but keep in mind only MAGES will be able to do so sense they are the only ones that can use it. Meaning a high level mage could use it from invintory, but no other classes.
Can the pet be summoned if the cape is in inventory, or does the cape need to be equipped? If it needs to be equipped, can it be placed into inventory once the pet has been summoned?
This Cape summons a pet whatever level the caster is, the one I created was a ^ golem. Casting time is around 1 sec but don't really remember. The reuse time on the cape is 15 min.