China Southern Airlines check-in window: Domestic online check-in opens ~14:00 the day before departure, closes 45-60 min before; international opens 24-48h before, closes 60-90 min before (route-dependent).
After checking in online you receive a mobile boarding pass; checked bags must still be dropped at the counter before the cut-off. International flights usually require document verification at the airport, so allow extra time.
At the airline's home base (Guangzhou Baiyun & Beijing Daxing) you'll find the fullest set of counters, kiosks and bag-drop lanes; at peak hours (7-9am, holidays) arrive 30 minutes earlier than usual. Seat maps are widest the moment check-in opens — window, aisle and exit-row seats (sometimes paid) go first.
For international departures check passport validity (6+ months is the usual requirement) and destination visa/entry rules; some countries also require proof of onward travel, which the counter will verify.