It does depend on whether you are first off or one of the last, but both as foot passenger and as cyclist, so between cars, I have experienced between a few minutes and at most 30 minutes. If you are the last passenger car of a full ferry and there are a few time consuming ones before you, it may take an hour or even longer.
If disembarking time is essential, try talking with boarding staff before you get on so you get a good position to be off fast.
But remember that arrival time is always weather dependant.
Credit:stackoverflow.com‘