Hourly subs blowing past the estimate - how I keep it from happening now

I had a similar run dealing with an hourly setter for a kitchen backsplash, and it was frustrating. I was working on a small section using herringbone pattern tiles, wich seemed manageable, but the estimate was for a whole wall. He kept moving onto the next section and then coming back, saying the last part needed adjustment. My original contractor quoted me $30 per hour for the whole job, and I quickly saw those hours ballooning without a clear end. What fixed it for me was being hyper-specific about the scope of work for every single payment. Instead of just saying 'tile work,' I told him I was paying him for the setting of one square meter of subway tile, and that's it. If he finished that meter, he billed me for it. He couldn't charge me for 'finishing' untill the next square was finished. This made him account for his time much more efficiently, because he knew he only got paid for completed sections. It shifted the focus from him trying to maximize his time on the job to me needing him to complete defined tasks. When he saw I was tracking progress in meter increments, the sudden extra hour charges started to disappear almost entirely. It’s all about making sure the unit of billing matches the unit of progress.

Only thing I'd add is the not-to-exceed number. When I had a carpenter sub on hourly, I told him upfront the job had a hard cap and if he saw us blowing past it, he needed to flag it before he kept working, not after. He actually appreciated it because it gave him cover when something ran long. Didn't have a single surprise invoice after that. Anyone else tried the cap approach, or does it just make subs rush and cut corners?

First time posting so hope this fits the thread. My situation was a bit diferent, hired a handyman hourly for a pile of small repairs last fall and never asked for any of this stuff, mostly because I didn't want to come across as difficult. Ended up paying for a fair bit of driving around sourcing parts. For those doing the daily notes thing, how do you actually bring it up without sounding like you don't trust the guy? Mine seemed easygoing but the invoice was still vague. Wondering if I shold just ask upfront next time or wait until a problem shows up.

Agree with the completed-sections approach, it's the only thing that ever worked for me on hourly jobs. I had a drywaller on an hourly rate for a basement finish and started paying per room: board hung, seams taped, that room's done. He stopped wandering between half-finished areas because he wasn't earning anything on a room until it closed out. One thing I'd add, I kept my own tally of finished rooms on my phone, dates included, so when the final invoice came we were both looking at the same numbers. Never argued about a single hour after that.