Generally speaking items with spell effects take much longer to cast than the spell itself.
Drones of Doom for example on ES vambs takes 8 seconds or on rowyls bracers 7.5 seconds compared to the actual cast time of 4.5 seconds. 3 seconds does seem a long time but I would be very surprised if its the same as the real spell.
Yes, usually a clicky buff has longer cast times than the actual spell. The only problem with that logic on this item is it is a spell that is only useful IN battle. With a cast time even 2 seconds it will be difficult to cast while you are getting beat on. Guess it isn't so great for Tanks after all /sigh