I have not been on SQ in a million years, but I have an award in Y for myself and little_1780 in a few weeks (its part of a greater UA itinerary/award). So some general questions:

How early can I check in with SQ at HKG & SIN?

While I was able to select seats in Y, does SQ offer any better seating at check in for a UA 1K? not necessarily looking for free, but I would take it. But any prospect of a cash upgrade to any better seating (premium Y, Business or F)?

Each of the 2 legs are only 4ish hours, so its not critical either way.

Any other thoughts or advice?