Koh Rong to BKK within 1 day?

Cheers fellow travellers,

Does anybody know if there is a possibility to go from Koh Rong, Coconut Beach to BKK within one day?

My hostel in Koh Rong told me to get to SHV the afternoon before and take the 7pm bus arriving at 2.30pm in BKK.

But I guess this is the one going to PP first. That would be quite awkward.

I am considering going by ferry to SHV, taking a bus to PP and a plane to BKK. But that's relatively expensive and I don't know about the ferry schedule.

The other possibility would be to go to SHV by ferry, to Trat by van or shared taxi and to BKK by bus. But I don't know how to get cheap vans/shared taxis and how to find fellow travellers. And I am also afraid I would reach BKK later than 8pm...

Thanks a lot!