I'd just use a timer function for a timer...
Code:
#include <acknex.h>
#include <default.c>

long lng_total;
var var_secs;
var var_mins;
var var_hours;

FONT* fnt_timer = "arial#24";

PANEL* pnl_timer = {
	
	digits( 60, 60, "%02.0f", fnt_timer, 1, var_mins);
	digits(100, 60, "%02.0f", fnt_timer, 1, var_secs);
	flags = SHOW;
}

void restart_timer(){
	
	proc_mode = PROC_LATE;
	lng_total = 0; //nanoseconds set to something to speed up time (55000 55seconds)
	timer();
}

void main(){
	
	timer();
	on_mouse_left = restart_timer;
	while(1){
		
		lng_total += timer() / 1000;
		
		var_secs = integer((lng_total / 1000) % 60);
		var_mins = integer((lng_total / 1000) / 60);
		
		wait(1);
	}
}