Why not just keep it as a DateTime Item instead of splitting it into hour and minutes. Then you can use DateTime List Item and DateTime Standalone Widget to modify it in MainUI. Note that’s just a really simple widget that just sets the properties to enable the built in Date Time Picker. You could adjust the properties to just show the time part and use the To Today rule template to move it to the new day.
This is written up in more detail at Creating Capabilities with Rule Templates: Time of Day.
At this point keeping up with separate Items for minutes and hours is just going to make things more complicated than they need to be any more.