Similar quandary here:
My chicks are 2 weeks old today, and I tend to regulate temp by how they behave. Since they've got a good-sized space with good ventilation in my garage (brooder is 3'x5', open sides), they have a wide variety of temperatures to enjoy. In terms of feathers, they're doing really well on their wings, but their heads, backs, and bellies are still pretty fluffy.
It's going to be 80*F tomorrow, and the brooder is in my garage. Once the garage warms up to the daily high, I worry that the heat lamp I'm using is going to result in baked chicken before I can get home from work at 5-6 PM. Today was similarly hot, and I just unplugged their heat lamp in the early afternoon and plugged it back in now that the garage is back to reasonable temperatures -- it's about 72*F outside, so ambient in the garage would be just a little warmer at the moment, and it'll all cool off to about 60*F in the night, so I want the lamp back on for that!
My options right now kind of look like unplugging the lamp in the morning and hoping for the best or leaving it plugged in and hoping for the best.
Thoughts?