I'm having trouble with getting the hour and minute commands down to one digit
Hour and minute commands? What are they?
If you mean hour and minute values, that's a different story. Divide by 10 to get the 10s place. Use the modulo operator to get the ones place.
Show one value at a time.
I want one button to display the time on one digit
Might I suggest that a switch would be more useful than a button. Unless you are making a shirt, I guess.