Suppose your SO sends you an email instructing you to be wearing something in particular when he gets home from work at five because sex. Suppose this is the sort of thing you've been wishing he would do (so it fits in with your fantasies) but has never happened before. Suppose, also, that he usually gets home at seven, and you had made plans to hang out with friends from 4-6ish but hadn't mentioned it to your SO because you were going to be home before him anyway.
What do you do? Do you ditch the plans with your friends? Do you email your SO back and say "I'll try but I might not be home until six? Do you go hang out with friends very briefly before rushing home for interesting sex? Any decision must be made by noon because, hypothetically, you're going to be stuck in meetings from then until four.