This should be correct:
* 10-16 * * 1-5 /path/to/my-script
So every single minute, between and including 10am and 5pm, every day in every month that is a day between and including monday to friday. Obviously "office hours" is a fuzzy expression, many people have other schedules ;-)
Unfortunately I fail to see an easy solution to get the script executed also exactly on 5pm...