My message...Our group of five is planning to visit Selayar in November 2017. We would like to take the ferry that goes from Selayar to Labuan Bajo, Flores. Can anyone confirm that the ferry goes once a week, on Sundays? Anyone know the name of the company which runs the Bira-Selayar-Flores ferry?

According to this site the ferry is operated by ASDP. It leaves Bira at 12 noon Sunday and arrives Labuan Bajo at 6 AM Monday.
https://www.indonesiaferry.co.id/eng/index.php

Both information on scheduled sailing times and actual sailing times can be highly unreliable. This is a car ferry, so not sure if it has cabin accommodation.

You might contact the place where you will stay in Selayar or Labuan Bajo for current information.

I've never made this trip but the thought of spending 18 hours on an Indonesian ferry is not appealing. Conditions can be quite rough and safety worrisome. If you can afford it, fly from Makassar.

Thanks heaps, Marmot-most helpful. Still might try the trip, even though 18 hours.

I hope you enjoy your time in that part of Indonesia. Come back and tell us about it.