I recently transferred some Chase miles to SQ and while the web site said up to three days it only took a little over 12 hours. I think the processing is due to Chase or AMEX in your case needing to transfer in an overnight processing cycle and SQ doing the same on their end. The time period may be dependent on the time when the transfer was started.

A transfer of AMEX to SQ got much better than a transfer to BA when AMEX and BA changed to only providing for 80% of the miles transferring. i.e.., 1000 amex becomes 800 when going to BA. Amex to SQ are still 100%.

I recently used Chase miles on SQ to return from Milan to AKL after the March 2017 Explorer crossing. Turned out to be a really good value for the miles and we ended up where we needed to be.