The Ward is just designed to momentarily stun people with a sudden and unexpected burst of Loa Magic. It's hard to avoid if you don't know it's coming, one major limitation is that it can only be used as a trap, I can't just throw it at your feet because you have to enter the 10ft radius (or whatever it was) after its already been activated.

It's up to you how long your character would be reasonably stunned for, though a second would probably be the minimum.