The best time to seal a blacktop driveway is when there's fair weather in the forecast. What time of year depends on where you live. The key is having mild temperatures and dry conditions that will allow the sealer to set.
Make sure there will be no rain for 36 hours before you start applying the sealer. Plan to be off the driveway for up to 48 hours.
Clear the driveway of all vehicles, vegetation, toys, water and pets. Remove grease and oil spots by washing the driveway surface. Patch any cracks or holes.
The outside temperature must be at least 50 degrees for the sealer to cure correctly. Some driveway professionals say 65 degrees is best. Temperatures above 95 are too hot because the sealer will dry too fast and may leave an uneven finish.
Allow six to eight hours for the driveway sealer to dry before you walk on it. If it's in a shady spot or if there is high humidity, do not walk on it for at least 12 hours. Don't drive on the blacktop for at least 24 hours, and allow 48 hours if there are cooler temperatures or high humidity.
Driveways with many cracks may take longer for the process to complete. Two thin coats of sealer are better than one thick one. So the best time to seal is when the weather permits and you've got the time to devote to the project.