not from Singapore. Transferring through. Some flights transfer through Singapore. If you have a flight that transfers through a country that has stricter guidelines, the airlines will hold you to those stricter guidelines. In my case I am transferring through Singapore which wants a test to be taken 48 hours or less before flying from my departure location.
you seem to be confused about what “two days” means in the context of these guidelines. It’s 48 hours. A “day” as in one full rotation of the earth measured from midnight to midnight starts and ends at a different moment existentially on every point on the earth (let’s say every time zone for simplicity). If it were “days” as it is in the country or local of concern as you seem to be utterly fixated on, you would lose half a day in flight alone. Don’t be silly and over dramatic.
the test is required to enter Thailand as well so that’s not really a relevant differentiation. The only thing that’s worth noting is that a connection through Singapore shortens the window to 48 hours from 72
yes. However they don’t really define what that is. In another section they refer to the fact that Hong Kong may require that you show proof of ISO accreditation or “relevant local authority”. However, no one that has been through Singapore has suggested it was so stringent. Just about any clinic or lab doing RT-PCR tests is going to be accredited and ISO certified.
I’m really not terribly worried about that. So long as it’s the correct test and in the timeframe window, I’m quite confident it will be fine. These are airline staff checking these documents. They’re just checking the boxes