I have similar observations. The time saved is things like going to some library I wrote to find the exact order of parameters, or looking up some API on the internet and adjusting my code to it. Inevitably if I did that the old way, I would screw up something trivial and get annoyed.

I rarely let it run for over 10 minutes unattended, but the benefits are not just pure time.

Being able to change the code without getting bogged down allows you to try more things. If I have to wait half an hour between iterations, I'm going to run into bedtime quite fast.

On top of this, I'm finding that the thing that takes the deepest attention is often, amazingly, trivial things. Fiddling with a regex takes attention, but it doesn't often decide the success of the project.

By contrast, the actual work, which is making technical decisions, is something I can do without concentrating in the same way. It's strange that the higher value thing feels less stressful.

Put these together and I'm more productive. I can string together a bunch of little things, and not have to be at my sharpest. Work can be scheduled for whenever, which means days are more flexible. More gets done, with less attention.