code: public static long start(String key) {
  
          if (key.isEmpty()) {
              throw new InvalidKeyForTimeStampException();
          }
  
          // current timestamp
          long timestamp = QuickUtils.date.getCurrentTimeInMiliseconds();
  
          // save the timestamp
          QuickUtils.prefs.save(TIMER_PREFIX + key, timestamp);
  
          return timestamp;
      }
docs: Start counting time
  
  @param key the key for the timestamp
  @return the timestamp