What is the safest late-arrival plan from a China airport to the hotel?

Handing over your passport at the desk is the hotel discharging a legal duty

Article 6 requires a hotel to register every guest, to inspect the identity document when it does, and — for a guest from outside the mainland — to file the registration form with the local public security organ within 24 hours. So the passport request is not the front desk being cautious or singling you out: it is the one step the hotel is not allowed to skip, which is also why a property that cannot do it will turn you away rather than bend.

Where in the source: 第六条: “旅馆接待旅客住宿必须登记。登记时，应当查验旅客的身份证件……接待境外旅客住宿，还应当在24小时内向当地公安机关报送住宿登记表。”

A late arrival does not suspend the duty — which is why the desk still has to be staffed

The registration and inspection duty in Article 6 attaches to receiving the guest, whatever the hour. A property that cannot verify a document and file the form at 02:00 cannot lawfully check you in at 02:00. That is the sourced reason a late landing needs a property that is genuinely staffed overnight, not merely one whose lobby is open.

Where in the source: 第六条: registration is mandatory and the identity document must be inspected when the guest is received.

If you arrive before you can check in, the custody duty already applies

Article 7 obliges the hotel to have guest property storage — boxes, lockers, a storage room or a safe — with a named person responsible and a registration, collection and handover procedure. So leaving a bag while you wait out the gap between landing and check-in is provided for rather than a favour.

Where in the source: 第七条: property storage must be provided, with a designated person and registration, collection and handover records.