Can international bank transfers be guaranteed at the time of execution?

In most cases, the answer is no.

International wire transfers are subject to manual review, and the very minute you introduce a manual review process, the committed timelines go out the window.

Also, most of the wire transfers are based on a batch of FIFO (First In, First Out) during operational times. The interdependencies with respect to the next bank in line that will take over the transaction baton and run with it, is always questionable. They might be having a holiday, so systems are down, or transaction was flagged by the correspondent bank, etc.

There isn't a universally accepted systematic method of guaranteeing transaction executions.