@Gaby Yes, 4k posts (especially if there are hundreds of photos) will probably take a little while. Minutes, not hours. I don’t have any estimate because it depends on so many things.
@Gaby Sounds like it got stuck. I’d cancel and start over. Also, I recommend creating a new journal and making it the default to import into for testing.
@Gaby Yes, Micro.blog uses the Day One command-line tool to send data to Day One, so that has to be installed for the import to work.