code: def on_for_seconds(self, left_speed, right_speed, seconds, brake=True, block=True):
          
  
          if seconds < 0:
              raise ValueError("seconds is negative ({})".format(seconds))
  
          (left_speed_native_units, right_speed_native_units) = self._unpack_speeds_to_native_units(left_speed, right_speed)
  
          # Set all parameters
          self.left_motor.speed_sp = int(round(left_speed_native_units))
          self.left_motor.time_sp = int(seconds * 1000)
          self.left_motor._set_brake(brake)
          self.right_motor.speed_sp = int(round(right_speed_native_units))
          self.right_motor.time_sp = int(seconds * 1000)
          self.right_motor._set_brake(brake)
  
          log.debug("%s: on_for_seconds %ss at left-speed %s, right-speed %s" %
              (self, seconds, left_speed, right_speed))
  
          # Start the motors
          self.left_motor.run_timed()
          self.right_motor.run_timed()
  
          if block:
              self._block()
docs: Rotate the motors at 'left_speed & right_speed' for 'seconds'. Speeds
          can be percentages or any SpeedValue implementation.