Give it a try! I can't (and won't) tell you what to do, of course. You are there and I'm not. You know your situation, your setup, and your personal comfort zone far better than I do. Yes, I do think turning off the light periodically is a good idea. What you're proposing seems like a huge temperature swing, from 72 degrees in the basement to the twenties outside, without some preparation for them. They are also going to be very, very mad at you when they experience darkness for the first time and you'll likely see your first real chick temper tantrum when the light goes out for the first time at night.
All of this acclimatization and light/darkness is why I don't raise chicks inside at all. I'm too lazy to want to do all that stuff. They go out and stay out from day one....well, actually I do keep them inside for the first day or so to make sure they aren't suffering any shipping stress or hatching stress, that they know where food, water and warmth are and then I move them out to wire brooder pen in the run. They have their Mama Heating Pad cave and that's what they depend of for heat, and they understand natural day/night cycles immediately and acclimate to the ambient temperatures on their terms, just as they do under a mama broody hen. So going from a heat lamp situation to the outdoors is a huge transition, yours are still young, and my inclination would be to wean them off heat and light before they go out. It doesn't take that long, but they really need that when they're raised indoors.
All of this acclimatization and light/darkness is why I don't raise chicks inside at all. I'm too lazy to want to do all that stuff. They go out and stay out from day one....well, actually I do keep them inside for the first day or so to make sure they aren't suffering any shipping stress or hatching stress, that they know where food, water and warmth are and then I move them out to wire brooder pen in the run. They have their Mama Heating Pad cave and that's what they depend of for heat, and they understand natural day/night cycles immediately and acclimate to the ambient temperatures on their terms, just as they do under a mama broody hen. So going from a heat lamp situation to the outdoors is a huge transition, yours are still young, and my inclination would be to wean them off heat and light before they go out. It doesn't take that long, but they really need that when they're raised indoors.