It depends on your market/ do a survery and ask!
I have a 7:30 am class that is well attended, but I agree with Stephen, most bootcamps are held early:
If you have a bootcamp that is based on 6 to 10 week comittment it makes those wee hours seem a bit more doable! Also, studies have shown that people who workout first thing in the morning have a higher retention level!
I have a 6:30 p.m. bootcamp that does well for working moms!