For floor use in Guernsey, check the underside after each night and decide how to air it from what you find. Regular lifting matters even on days when you cannot take the futon outdoors. A fixed weekly schedule can miss a damp contact surface between airing days.
What is the first check in the morning?
Lift enough of the bedding to inspect and feel the underside and its base. If either is damp, give both time to dry before putting them together again. Do not fold damp bedding into a closed storage space to clear the room quickly.
Does airing also mean changing its position?
Use the other face and turn the bedding head to foot regularly so one area does not take the same pressure every night. Choose dry outdoor conditions when practical; otherwise arrange indoor airflow around the underside. There is no universal number of minutes that proves the inner filling is dry.