How to display a timer in a Cocos2d game? -

i'm trying display timer in cocos2d game shows number of minutes:seconds:milliseconds user has spent on level. i've searched examples , found should not using nstimer. understand should using cctimer class, i'm having tough time finding decent examples.

//declare in interface cclabelttf          *mtimelbl; float               mtimeinsec; 

//init in onenter

 mtimeinsec = 0.0f;  [self schedule:@selector(tick:)]; 

//function used

-(void)tick:(cctime)dt {     if(self.isgamepaused || self.isgameover)         return;      mtimeinsec +=dt;      float digit_min = mtimeinsec/60.0f;     float digit_hour = (digit_min)/60.0f;     float digit_sec = ((int)mtimeinsec%60);      int min = (int)digit_min;     int hours = (int)digit_hour;     int sec = (int)digit_sec;      [mtimelbl setstring:[nsstring stringwithformat:@"%.2d:%.2d:%.2d",hours, min,sec]];  }