The main problem here was already stated. Dungeons are meant to be an in and out affair. From the devs own mouth if a run goes past 20 minutes either your party has some explaining to do or the devs really messed up. "Expert" dungeons as they function now just aren't the place to add these mechanics in. Stop thinking "How do I slow this run down" and instead start thinking like a game dev. "How do I make this more addiction/fun. The end goal is still make you play longer, but slower just means you'll lose players. Addicting, now that's the key