All day, every day. It can stay on your lens at all times.

A UV filter doesn’t affect your camera’s exposure settings, so you can leave it on your lens at all times with the added benefit of it acting as a protective layer over your lens glass. Some pundits say that the extra layer of glass over your lens degrades image quality and can cause lens flare, but using premium quality lens filters can avoid these issues. Ultimately, you need to weigh up the risks and rewards. Keep in mind the difference in cost between replacing a scratched lens filter after a misadventure while shooting versus replacing the entire lens. If you shoot indoors all the time and don’t want anything to come between your lens and your subject, you can definitely take off your UV filter.