Not very long, a couple of minutes maybe.

[ But still, it's a few minutes more than he could do before. And the matron of the house had been pretty proud he could do it at all and said with practice, he'd get better at it. The praise from Wanda feels a little more impactful to him, especially right now. ]

Flashlight is a good way to put it. I can't control what color it turns, but so far I've seen green and blue.