We did a Sydney to Auckland cruise on Celebrity on 2016. One of the options was an overnight from Milford Sound to Dunedin. We basically got off the ship in Milford sound with an overnight bag. They took us to various sites along the way. We stayed in Queenstown, visited a sheep sheering event, had dinner, stayed in a very nice hotel. The next day towards Dunedin we stopped at a bungy jump place and had the opportunity to do an on your own but passed. I think we also stopped at a winery but don't remember. We arrived in Dunedin, and rejoined the ship.
They had an upgrade to the extension where instead of being in a bus you were in a minivan with more intimate experiences.
I am glad I did it. I don't know other cruise lines provide that option.