If you’re only teaching one time each day, the earlier the better. I agree with Christine about 5:30-6:00; that’s early enough so those going to work or taking care of family to get to the gym and back home for their daily responsibilities. Earlier than that, however, is a hard sell; most don’t want to get up earlier than 5 AM to start their day.
Beyond that, your time of 10 AM could be just as fine. You could get feedback from those wanting to take the class, if possible to see if it or another time would be a good fit.
I teach 3 classes during the week that start at 5:45 a.m. They are my biggest classes because many people want to get their workout done for the day and then go to work. So , I guess to answer your question, probably somewhere around 5:30 or 6 a.m. would be my guess for the earliest start. Just depends on your location and market.
Your time of 10 will also work well for those with a flexible schedule and stay at home moms.
Hope this helps and good luck!