Gotcha. So they're out full time now, then? If they're in the coop and haven't had heat during much of that time, you might as well try going without heat in the coop now as they shouldn't need it if they've been acclimating fine without it.
I'm still confused - if there's no heat provided why is there a light on at night? They do not need light at night but optimally you want to dim it gradually so they can settle down and go to sleep.
The light is a LED bulb right? Even incandescent adds heat. Asking for clarification because...
Bring them in at night if needed for the first few days but no heat should be needed at all indoors. You need to fully wean them off heat and get them acclimated to the range of outside temps so you can move them out of the brooder before the new batch arrives.
Are any of the chicks runty or unusually feathered (i.e. Silkies)? If they're all standard breeds, with those temps I'd be working to start move them outside, now. They can handle those temperatures just fine at 4 weeks when properly acclimated. That means cutting off heat indoors for starters.