I have a 20% off booster for my personal train. It's instead 20% *of* the wait time. My maintenance time is 90 minutes, so 20% off is 18 min, so the time should be 90-18=72 min. But instead, my maintenance time is 18 minutes.

This has been a bug for a long time now, and I'm surprised it's still there.

Also, I activated the booster right after using my personal train. When it activated, the train was immediately ready.