I am considering a 13:30 arrival at Changi on one ticket and a 20:00 onward flight on another, with a checked bag and a possible terminal change. I would like to leave the airport for dinner but feel uncertain about whether a landside check-in, baggage collection or overnight plan changes the documents I need, so I want to decide before buying either ticket.
The key decision is whether I can remain in the designated transit process with an onward boarding pass and baggage handled airside; collecting luggage, checking in landside or leaving for dinner makes Singapore entry rules relevant. Ask each airline about baggage transfer, terminal movement and boarding-pass issuance, then check ICA for the passport and travel date. Checklist: passport, onward booking, baggage plan, accommodation if staying overnight and any required arrival declaration. A long layover or separate tickets can change the answer, and airline handling is not a substitute for immigration permission: https://www.ica.gov.sg/enter-transit-depart/entering-singapore.