This is what our temps have been doing the last few weeks too. It’s been mid 70s with lows in the mid 50s. Starting Sunday, we’re in for about a week of 80° days. We’ve had the AC off for about 2 or 3 weeks. I don’t know anyone who ever runs their AC & heat in the same day either. It seems like a huge waste of money… pay to heat the house then pay to cool it a few hours later. I’ve had the windows open for weeks, it’s generally been from 67 - 77 in the house. I’ve closed some curtains to help keep the house from getting too hot. Or closed the windows earlier if it’s supposed to get too cool that night. Our furnace can run just the fan, no heat or AC. So I do turn the fan function in if it’s getting too stuffy at night, helps move the cooler air from downstairs up to the bedroom.
Many years I’ve needed the heat on by the middle of September, even just for an hour or so to take the chill out. The last few years since our fireplace was converted to gas, I light that when I get up instead. I think this is the latest we’ve ever gone without needing some kind of heat on.