[Slice]

I used GetTickCount.

pawn Code:

#include <a_samp>
#include <timerfix>

main() {
    SetTimer("TimerFunc", 500, true);
}

forward TimerFunc();
public TimerFunc() {
    static
        previous_call
    ;
    
    if (previous_call)
        printf("Previous call %dms ago.", GetTickCount() - previous_call);
    
    previous_call = GetTickCount();
}

Try it out for yourself, both with and without timerfix.