@TIMER's format specification is not honored if the timer is not running.
Code:
v:\> timer /1 on
Timer 1 on: 16:46:26
v:\> echo %@timer[1,ms]
2493 ms
v:\> timer /1 off
Timer 1 off: 16:46:34 Elapsed: 0:00:07.784
v:\> echo %@timer[1,ms]
0:00:00.000