A:
According to page 12 of the manual, 1. Touch Stop/Clear so that time of day appears, then 2. Touch Start/Enter and hold until "LOCKED" appears (about 4 seconds). To cancel, touch Start/Enter for about 4 seconds until "LOCKED" diapears and time of day returns.
IMO: This would only be good for use with small children who do not see you do this.