Complex sentence: If the compatibilist says "I may visit tomorrow, or I may not", he is saying he does not know what he will choose--if he will choose to follow the subconscious urge to go or not.
Split into simpler sentences: If the compatibilist says "I may visit tomorrow, or I may not". He is saying he does not know what he will choose, If he will choose to follow the subconscious urge to go or not.