Preference File

import time
self.startTime = 0

STATUS.connect('periodic', self.set_timestamp)
STATUS.connect('command-running', lambda w: self.get_time())
STATUS.connect('command-stopped', lambda w: self.stop_time())

def get_time(self):
    self.startTime = time.time()
    self.timerOn = True

def stop_time(self):
    self.timerOn = False

def set_timestamp(self):
    if self.timerOn:
        self.w.labelWidget.setText(time.time() - self.startTime)
    else:
         self.w.labelWidget.setText('Run Timer Off')