Как сделать в секундомере часы и минуты?

    def tick(self, *_):
        if self.time >= 0:
            self.time += 1
        else:
            pass

    def start(self, *_):
        self.cb = Clock.schedule_interval(self.tick,1)

    def pause(self):
        Clock.unschedule(self.cb)

    def reset(self, *_):
        self.time = 0

class CrudeTimerApp(App):
    def build(self):
        return CrudeTimerGrid(time = 0)