Hansel pushes a 2 lb. box 5 feet in 20 seconds. How much work has he done?

Work = force x distance

You can see time doesn't matter (if we were talking about power, which is the RATE at which work is performed, that would be a different story).

W = 2 x 5 = 10 foot-pounds of work

Foot-pounds are gross units. Better to work in SI units when you can!