You want your workers to compile the code before committing it and moving on to the next task, right? But don't feel like you should pay for that?
Or are you assuming that people are like fleshy machines that can just store the data they just used on disk and work on something else while the compilation is running and then they just put that data back into RAM once the compilation is done? People don't actually multitask that well.
> [...] some of this idle time is spent thinking about problems to solve related to the job, but it's something that can be done in your free time, or while commuting.
Now that just sounds like you don't feel like you should pay workers that do intellectual work for their work at all – they can do their work in their "free" time? By that logic I don't see why you don't just pay for the 1 minute it takes to commit the code once it's finished – in the end that's all you care about. Why would it be your problem how they get there?