I did two DSDs on vacation in Australia before I even knew there was a local diving community.
I learned two things on those DSDs, I loved diving and hated cattle boats. The boat I was on had about 50 passengers, about half of those were doing DSDs, and they took 8 divers down at a time (in separate groups). Looking back on that with the benefit of the experience I have now, I think they ran a very efficient system and were well organized, but it was still a very long day for 2 15 minute dives.
The worst part was that in spite of being warned that if anyone starts to feel seasick, to get out to the back of the boat. A few people ignored this and puked into plastic bags inside setting off a chain reaction where a lot of people were sick. So, despite the cold ocean breeze on the evening ride back, I froze my ass off sitting topside for the duration.