This rule applies to both quartz and automatic watches. You should avoid manually changing the date during these hours (the "danger zone") because the watch's internal gears are already engaging to advance the date automatically. Forcing a manual change while these gears are locked can break the delicate teeth of the movement. Pro tip: To be safe, always pull the crown out and move the hands to 6:30 before setting the date, then reset the time to the correct hour.