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There may be something better (or more simplistic), but I use Hurdlr for this sort of thing. Since it is for a business, he may even prefer Hurdlr. You can set it to auto start/stop a few different ways or set it for manual start and stop. It's been as or more accurate than any other tracking app I've tried.
It has client and note sections on each trip, as well.
Hurdlr app has worked well for me.
I use https://play.google.com/store/apps/details?id=app.hurdlr.com track the miles from the tone to you leave tell you get home plus expensive and earnings.