Creating a simple drop-down list

This is probably so easy, but I my brain must be on vacation today.

I want to have a series of cells where, in each cell, you can use a drop-down list to select a time from the list (this is for a work schedule worksheet--we have noticed a problem id someone types in 8am or 8:00am in stead of 8:00 am so we want to make it easy with a drop-down list).

Can anyone help me make the list and then the drop-down feature? Thanks!