welcome to the forum! are you using a UVB light? how will the sulcata be getting the UVB? posting enclosure pics will also be helpful! if you are not providing a UVB light, then 3 hours a day of natural light is good.
If you're talking about the sun shining in through a window, then no...that's not enough UVB and you still need the light. The glass on the window filters out the UVB.
Welcome to the Forum. Exposure to sunlight is good for your tortoise. Be sure that they have some shade so they can move out of the direct sun when they want to.