If you are playing EEs it means you have a bit of knowledge of the quest you are doing and cast Displacement as you run toward a group of mobs.
If the quest is your first time on EE, you just try to keep yourself displaced and/or, if you have limited clickies, you cast it as soon as you see the above group of mobs.
In any scenario, you don't need 10 seconds to cast displacement. Don't even need 5.