Hello, ohmbru2.
May not get exactly what you want. But, ctrl+shift+":" can be simulated exactly by:
Sub macro() 'or give it a better name
ActiveCell.Value = Time()
ActiveCell.NumberFormat = "h:mm AM/PM"
End Sub
To even more closely simulate it, you can assign a shortcut key which, however, must be of more restricted form of ctrl+<a letter>, say, for instance ctrl+"t".
regards - tsuji