This worked:
su discourse -c 'bundle exec script/discourse remap //discourse-test.example-domain.com //talktime.example-domain.com
… and ran OK…
But the avatars not did port over in this restore process (we selected include images in the backup).
Update:
We got the avatars to work by porting over the images from server 1 to server 2 from here:
/var/discourse/shared/standalone/uploads/defaults