Hi,
I think restrictions have been relaxed since 1st April and if you are vaccinated you do not need a test on arrival ( you need a pre departure test though)
https://www.channelnewsasia.com/sing...etired-2582986
You could do a lot in three days but it is a long flight with time zone differences but it is a fascinating city ( hope to go there for 2 weeks in June/July)
Regards
TBS