I reverted it back to the previous style. 

*My original intention was that the keydownEvent knew the implementation details of incrementing/update hours/minutes/etc.*

The keydown event was specifically listening to up/down. You can translate that more clearly in english by the handler knowing that they want to change the hour up or down by one per keypress. They don't have to know anything about passing a 1 or -1 or anything else.