A few factors can influence how long it takes to disembark the ferry, such as the size of the ship, the number of passengers and vehicles on board, and the time of year you are travelling.
Disembarking will typically take between 15 and 45 minutes, but there are no guarantees.
You should also allow extra time to exit the port, especially for international crossings and peak travel dates. If you're booking a connecting journey, make sure to give yourself plenty of time.