Can each item in drop-down list REPRESENTa value that will populate the cell?

My Excel operators are running a real-time itinerary process. I have designed dropdown lists for their convenience that names the times of the day in half-hour increments. But the operators are uncomfortable with the use of 24-hour military time, and this is the time value necessary for logging hours-worked from a bookkeeping perspective.
Is there a way in which the operator selects a familiar 12-hour (AM/PM) time from my dropdown list and have the selected cell automatically populate with a corresponding 24-hour-clock equivalent?
Cheers,
jeffery_g

Hello ChemistB:
That's it! Your example will do exactly what I want...
Thank you so much for the expertise.
Will mark this thread as "solved".
Cheers!
jeffery_g

THE SOLUTION: My drop-down list...

A1: 1:00 AM
A2: =A1+0.5/24 [1:30 AM]
A3: =A2+0.5/24 [2:00 AM]
A4: =A3+0.5/24 [2:30 AM]
...etc.

Thanks again, ChemistB!