I may take some "heat" for this, (ha ha, couldn't resist!) but I actually think cooler temps in flowering promote trichome development. As flowering progresses, I try to keep the temps lower than in veg mode, but not under say 68F. My past outdoor grows have had temps go down into the low 30's at night with little to no harm to the plants and they seem to get really frosty. In an indoor grow I don't think you need to go that low, but a few degrees colder imo can help the potency a little. My 2 cents...