Yep, though in hot weather making a lawn wait an extra day may be bad. Last time I missed a day my grass looked bad and I had hundreds of dead worms on the sidewalks. I assume the ground got too dry for them and they tried to flee. The grass did recover but I felt bad for the worms.
To your main point it would be nice to be able to specify the watering hour restrictions and have it work around those. Personally I like my watering to be done by a certain time each morning so I have to set my flex start time far enough back so that if all of them were to run on the same day. On days when only a few zones run it does start earlier than I'd like so by the time I get up I can't tell if it really ran. So a low priority wish list item would be picking an end time and having Iro dynamically pick the start time.