INT F7 - FSBBS 2.0 - TIMER FUNCTIONS
        AH = 05h
        AL = function
            00h get time remaining
                Return: DX = number of minutes remaining
            01h get current time
                Return: DS:DX -> 8-character time string
            02h increment time
                DX = number of additional minutes
            03h decrement time
                DX = number of minutes