Migration between iMacs stalled at 1 hour remaining for over 8 hours

Migrating between 2 iMacs (2012 and 2020 both running Catalina), using thunderbolt cable. About 1TB to transfer in total. It’s been stalled at ‘1 hour remaining’ for over 8hours. How long do I leave it? I have got Time Machine back up but it’s on an external hdd so super slow. Think it would take days using that …

[Re-Titled by Moderator]

Original Title: Migration has stalled