How do you keep plants warm with the dry start method? I turn my heat down to 62°-ish at night because the upstairs bedrooms get unbearably hot. (It's just minI dwarf hair grass.)
Being in a sealed tank, they should be warm enough without any concern. However in saying that I've done dry starts were the temp is around the low 70s F and then once flooded, temp is around 80F. They did fine, its a lot more important to worry about humidity then heat - heat normally just 'speeds things up'.
You could also consider wrapping the tank with towels to retain heat if needed.