Took Colonia Express earlier this month, we were told to check in at the terminal in BsAs 90 minutes before the scheduled departure time.

It was easy to check in with the self service kiosks (similar to what they have at some airports.)

It seemed like there was only one class of service, it was no frills and on time.

P.S. fares for Colonia Express and Buquebus ferries are lower on the Uruguay side of the websites.