The 6 month validty has been around for some time. In 2016 we went to Australia with SQ. We made a 12 hour gap in SIN to make a quick city tour.
At T2 check in they threatened to not let me board. Oz was happy with less than 6 months in the passport (I had checked) but SIN was not. Not even for transit, as I might have done a runner - although with the SIN Police, no sane person would try it.
SQ made me sign a form to absolve them of responsibility, and I signed to be a good boy. Then I got my boarding pass. This was clearly a SOP for them as they had a supply of the forms! So my companion did the tour and I enjoyed Changi airport.
With the current problems of countries closing boarders, probably not worth the risk. I did use the one day service in London once and it was very good.
Last edited by PAXboy; 8th Sep 2021 at 16:36.
Reason: last lines.