With those kind of temperatures you don't have to brood very long at all and can even turn off the heat source for most the day. If it's a warm spring we turn chicks out to coop at 3 weeks of age and those temps are nowhere near your heat.
Overheating brooders is a common problem. Provide plenty of space in brooder for chicks to move away from heat source and keep an eye on panting. Brooders are either too small or heat lamps too large being the culprit. Back when we brooded small batches of birds I'd only use 75W or even 60W incandescent bulb to one side of large plastic tote. Now we use a water trough for brooder in unheated garage and 125W heat lamp.
Overheating brooders is a common problem. Provide plenty of space in brooder for chicks to move away from heat source and keep an eye on panting. Brooders are either too small or heat lamps too large being the culprit. Back when we brooded small batches of birds I'd only use 75W or even 60W incandescent bulb to one side of large plastic tote. Now we use a water trough for brooder in unheated garage and 125W heat lamp.