Why are you defaulting to 59 minutes if the process was running before the hour started and finished after the hour ended?

A process that is already running at 12:00 and is still running at 1:00 was running for 60 minutes from 12:00 to 1:00, not 59 minutes. Likewise, if ti started at 12:30 and was still running at 1:00, then it was running for 30 minutes, not 29 minutes, during that hour.