jm ªZèQòÛLN· §UÛn°j].gñN7u+7L§From my experience, the tx is near instant via bitsocket https://twitter.com/_unwriter/status/1055472099681284097 - so I think the tx pre-build approach should work :)
https://whatsonchain.com/tx/fadb9b28e837521115442531b79c1222b9a079a5021d2b47128b739d6bae56ab