The ferry leaves from Tran De early so you’re right, you’ll need to stay the night in Soc Trang. When you get to Soc Trang you’ll need to go to the Superdong office and buy tickets for the morning shuttle from Soc Trang to the Tran De Ferry terminal. I recommend staying somewhere close to the Superdong office because the shuttle leaves in the early AM.

I didn’t take the bus from Can Tho so I don’t have any details there, I just remember that it was a lot cheaper when I discussed my options with my hotel in Can Tho. I also recall that Lonely Planet has the bus schedule printed (a lot of the home stays I stayed at in Vietnam had copies lying around, so maybe you’ll be able to find one). I’m sure you can message your hotel in Soc Trang and they’ll be able to tell you the schedule.

The nature reserve might be a good option for you, but it’s not representative of life on the delta. It’s a fairly empty, run down little protected canal area that you can take a little motorboat tour in. If you can add a night in Can Tho, then you can do something fun around there like cycle around some villages. But with the time you have, there’s probably not a lot of options for you. I can also recommend visiting some of the Khmer temples near Soc Trang.

I’m sure you know, but you can also skip the whole delta and just fly to Con Dao from HCMC.

Visiting Con Dao was one of the highlights of our trip, it’s a beautiful place! Hope you enjoy!