Set starting time in Time dropdown of DateTime component

The DateTime component's time entry starts at midnight and the user has to scroll a long way to get to the more commonly used times. Since the users will mostly use a value around normal working hours, it would be very helpful to them if I could set the time drop down to start at say 8:00am.

I know I can set the default to today (or other date) at a particular time, but my users will rarely select today.

I can do this with separate date and time components, but then I have the task of merging them together for all of the my inserts and updates.