You can.

You would need to change the TimerConst so that it interrupts at 1khz.
You can use mister-e's calculator for that.

Change the Ticks variable to a WORD.

Then in the ClockCount routine, change to this ...
Code:
    Ticks = Ticks + 1
    if Ticks = 1000 then
       Ticks = 0
       Seconds = Seconds + 1
; etc.
Happy Holiday's,