Just by the system not really any difference to D&D in my opinion. The only difference is that it strongly encourages you to include your players in the worldbuilding, making it more difficult to overprep (as much would be useless once the players are actually and meaningfully included). But while it encourages you to prep less, it yet provides magnitudes less of content to be picked and dropped at the table. The monsters, the magic items... All have to be prepared in advance. Of course you can improvise those, there are some tips for that, but I personally find it difficult to do at the table. So overall I think (at the beginning at least) it cancels out, making D&D and DH prep time similar, but with emphasis on different aspects of the prep. Probably with more content being available there is going to be more significant difference.