Currently based in SIN, I need to travel to CGK, collect an item (something important for a wedding) from someone at the airport, then fly to KUL to attend said wedding.

Since I have time, I thought... why not make a joy ride out of it and spend as much time as possible at TPR.

Hence the itinerary I'm brewing is as follows:
Day 1 - fly SQ Y SIN - CGK (morning), then
Day 1 - fly SQ F CGK - SIN (18:10 - 20:55) and I return home during this layover of less than 24 hours, then
Day 2 - fly SQ J SIN - KUL (16:25 - 17:35) because no F on this route.
CGK - SIN - KUL will be part of one F/J ticket. SIN - CGK is a separate Y ticket.

I know it's possible to enter TPR after arriving in SIN from CGK on Day 1.

Questions, if anyone knows:
- Can I can enter TPR also by showing my CGK - SIN boarding pass BEFORE departing from SIN on Day 1? (arguably I'm "arriving" in SIN on the "same day" )
- Can I enter TPR also on Day 2, on the basis of my CGK - SIN boarding pass, where my SIN - KUL flight departs "within 24 hours" of arriving in SIN the day before?

Just attracted at the novelty of this idea.