Are international money transfers truly instant?

Domestic, yes, international, no.

The cross-border payment rails are based on correspondent banking and Nostro accounts. They are usually batch processed, sequential and follow East to West sun cycle. So if something goes wrong in a transfer, you have to wait for the next day.

There are new companies propping up that do instant transfer or near-real-time transfers, but they are so, so, so, so, small in size and volume, they are not noticeable at the moment. Think of the current money transfer system as the old 1950s television set. The need of the hour is a HD 4k curved 3D TVs. We are doing all we can to run HD videos on 1950s technology and it does not bode well.

To answer your question: Money Transfers do not go through straight away. They can be hacked to make it seem they did, but the money is usually batch processed.