Why does the diagnosis take longer than the estimated time?

The diagnosis by default is only meant to take a couple minutes for each item that needs to be scanned and this is what estimates are based on

Some batteries in certain brands of laptops (HP is one of the most common) do not return their battery discharge information on a frequent schedule and because of this Battery Optimizer must run the diagnosis for longer periods of time for each device scanned, to be able to gather the required information.

Rest assured, you should only have to run a diagnosis once. After this you will be able to use the results gained from the diagnosis to determine how much time you can save by optimizing your computer’s settings.