get your daytime temp up with maybe a space heater, then at night 57 would be sufficient. If your night time temp gets 15 degrees below your daytime temp, thats when you can have fluctuation problems.
I've been using the one i bought recently, but it was giving me issues and shutting off randomy. I plugged it into a different outlet today so well see later what the temps have been now that itll stay on. I'll keep it on for a while bring up the temps while lights are on too. They're looking healthy tho.