There are many ways to do this, but I would do it top-down.
Start with working out how many people get their hair cut in a specific amount of time, and make an assumption about % utility of hair stylists.
i.e. Number of people in New York * number of times they get their hair cut per year * duration of a haircut = number of hours hair stylists spend actively working, which you can multipy by average price for the market size.
To work out opening hours and number of task force working, you can make an assumption on utility - I'd say 80% based on personal experience. You can divide the product from above by 0.80 to get total hours stylists work, and make an assumption also on admin (e.g. one full time per 4 stylists, or something similar). Assuming all staff work full time at 35 hours weeks, you can work that out by dividing the total product by 35.
Finally, you already have the total number of hours worked by all staff so can work out opening hours from there.
You can make it more nuanced by making assumptions about how many people have their hair done at salons vs. at home/by a friend, and you can also segment by, say, males and females (as this would impact both price of haircuts and frequency).