Impulse requires time, there's no calculation of impulse that ignores time.
It is often calculated with a duration of 0, but it is still calculated with time.
Can you please elaborate why it is not a change of momentum of a period of time?[/QUOT
In your own formula you've mv1-mv2 - so there's no time in there. I accept that the change does take time, but time doesn't affect the value of impulse.
If you divide by time, then you have force which is a different quantity