I'm not sure in what climate do you live, but 2 cents from me from Eastern Europe.
We have a lot of days when there is a sun without any clouds, and watering during daytime, not at early morning or at evening, is not a good idea at all. Water creates micro-lenses that allow sun to "burn up" everything in the garden.
Therefore, the best idea is to schedule watering to evening, night or morning time. Perhaps it's not the time when gardener comes in.
Maybe it would be better to negotiate program with him, schedule it for night - we at our area have 50% electricity discount from 11pm to 7am so doing all things related to watering after 11pm is even cheaper - and after few weeks of trials, when he comes and can possibly review and add water manually if it's not enough - came to good water schedule, that will not require any manual attention and BTW you will not need to pay him for the time he just starts program and waits for it to finish?