I would try and leave your mice in the cage, and if a fight starts, then, or coarse, take them out. If they are fine, then, don't leave them unsupervised. After YOU feel that they are used to eachother enough, let them stay with eachother and check constantly on them and make sure that everything is all right.

That is what I would do, but, I'm not an expert, so...If you don't want to try that, it is perfectly fine by me!

Good Luck