At P&O Ferries Hull to Rotterdam, for all passengers, including foot passengers, check in closes 90 minutes prior to departure.
On Stena Line ferries between Harwich and Hoek van Holland, all passengers must check in no later than 45 minutes prior to departure.
My experience with foot passengers on this kind of ferries is that the foot passenger terminal is deserted, as most passengers travel with a vehicle. This was true for Nynäshamn–Gdańsk and for Hoek van Holland–Harwich. Then why do they close the checkin 90 or even 45 minutes before departure? There should be plenty of time for foot passengers to get on board when arriving 30 or 20 minutes before.