To set a day-date watch correctly, never adjust the date or day between about 9 PM and 3 AM, because the movement is engaged to change over and forcing it can damage the mechanism. Set everything away from that window and you'll be fine.
Why the danger zone matters
In the hours around midnight, the watch's gears are partway through automatically flipping the date and day. If you manually quick-set during that window, you can chip or break the tiny change-over parts. Keep all quick-setting outside roughly 9 PM to 3 AM.
Step 1: Move the hands to a safe time
Before anything else, pull the crown and turn the hands to a safe position like 6:00. This guarantees you're clear of the danger zone while you make your adjustments.
Step 2: Understand the crown positions
Most day-date watches use a crown with two pulled-out positions. The first, or middle, position quick-sets the day and date. The fully pulled-out position sets the time and stops the seconds. Check your specific watch, since directions vary by model.
Step 3: Quick-set the day and date
With the crown in its quick-set position, turn it to advance the date and, if separate, the day until both are correct. Some watches change the day by turning one direction and the date the other. Never do this inside the danger zone.
Step 4: Set the correct time
Pull the crown fully out and turn the hands forward. To land AM versus PM correctly, cycle the hands past midnight once and watch the date flip, which confirms you're in the right 12-hour half. Then continue to the current time.
Step 5: Push the crown back in
Once everything reads correctly, push the crown all the way in. On a screw-down crown, gently screw it back down to keep water resistance. Don't force it if the threads don't catch.
A quick habit that protects your watch
Make it a rule: set the time to 6:00 first, adjust the day and date, then set the real time. That simple order keeps you out of the danger zone every time.