My cold treatment area is an unheated window with a shoplight hung above them. Nighttime temp certainly goes to 50, and anything 50 and above should be fine for night. Daytime would hit 60 to 65 this time of year. And the lights, although fluorescent, they do give off enough heat to be noticeable right next to the seedlings in a room with no other heat source.
The only concern I would have about flipping day for night, you do want them to be colder at night than in the day. They need 8 hours of darkness and the natural cooling cycle is the best. OTOH if you monitor your temperature, that may work out fine with the flip at least until it starts to warm up.
As regards the slower growth, this is true for sure, but last year I experimented with growing them up in a warmer room upstairs, that would have nights around 60 + and days 65-70 or more - sometimes shooting up a lot if the sun decided to shine.. They grew way too fast. I'm back to the basement.
