I TRY to bill on the half day/day or ideally for the entire project. But, if I have to bill hourly then the moment the clock starts an hour has begun. If I only work 10 minutes that day, then I bill the client an hour. If I work 10 minutes at 5 different times during the day, then I typically consider that all to just be 1 hour. If I do it 7 times, then that's 2 hours, etc.

I've also started a passion project to help aggregate data and stories like these. So far, only aggregating that data. https://hourly.fyi/