This is a question that I get asked a lot. The technical answer is an hour after sunrise or an hour before sunset.
My photo shoots are usually around those times, but I have shot in the middle of the day indoors through a window, under trees, or in shade.
The real answer to this question is, when you need to take them? If you need a specific time, I can make it work. If you are flexible, try 7:30-10am or 4-6pm depending upon time change.