Formula to not count hours before and after a specific set time period

If a person starts work at 9am (for general non selling items) and finishes at 5pm but doesnt start to sell until 10am and their sales per hour our based on the time the store is open to the public (10am -5pm) how do I not count the non selling hours (from 9am-10am) but still show the hours worked between 10am and 5pm.

Thanks for your help in advance

Hi!

There was a similar problem not long ago:

http://www.excelforum.com/excel-gene...f-the-day.html

I changed the solution a bit to fit the desired hours for your problem. See the attachment.
Hope it is the solution you were looking for!