Unlike any other value, the seconds can only be zeroed. Should this happen before 30 seconds, the watch will zero in at the beginning of the current minute. After 30 seconds it will start the next minute as displayed.
The seconds are unique in that they can only be set to zero. If this happens before 30 seconds, the watch will reset to the beginning of the current minute.  After 30 seconds, it will begin the next minute display.