This is very much dependent on your needs.
My normal working hours are between 11 am and 5 pm Monday to Saturday, but as above I can work to your schedule. For example it maybe convenient for you in the early morning before you get busy, or late at light – Especially if business operates through the night.
The same can be said for how big the commission is – It may take more than one day to complete the shoot, in which case it could be split into smaller sessions to fit around your schedule.
All of this would be worked into the shoot plan as part of your consultation process
If it’s an outdoor shoot then as a guideline I normally recommend, that it’s best to do the session the morning or late afternoon to get the best out of the natural light, but ultimately I will shoot at the best time for you.