Ok, for the first part, how how long can you keep the seal going/ when will you tire out. Describe what will happen when you experience this mental exhausted.
5min will not do i think, try to put a post count in it, same goes for the amount of days. Also, im nnot sure of the memory lost thing, thats like having two geass in one.
Now for the weakness part, add something like a body experience, like Rollo for example, his heart stops when he uses the geass. It doesnt have to be that extreme, just trand add something like blurred vision, or numbness to the point where you can barely move or grasp objects with your hand.