I thought he proposed before the job offer?
It does seem very sudden though, have they learned nothing from what happened with him and Amber? Not to mention Daniel and Imogen have been an "off and on" couple for a while now, why rush into marriage?
I'm gonna be so annoyed if they get married only for them to break up a week later. I've not read anything about Daniel leaving, but Neighbours do keep things pretty hush hush these days, especially departures.