Which of these is NOT a proper time to apply the parking brakes?

Applying parking brakes when the brakes are very hot is not advisable due to the risk of damaging the braking system. When brakes are hot, the brake components—such as drums or discs—expand, and applying the parking brake can lead to them becoming stuck in place. This could create issues such as uneven wear, potential damage, or difficulty in releasing the brakes later.

In scenarios such as needing to stop for less than one hour, testing the parking brake, or parking on an incline, these situations would warrant the use of parking brakes. Short stops and testing brakes are common practices where engagement of the parking brake can prevent movement. Similarly, on an incline, using the parking brake is crucial for stability and safety, ensuring the vehicle does not roll backward or forward when parked. Thus, applying the parking brake is inappropriate specifically when the brake components are overheated.