Well, lets see ... You need to progress your relation with Janice, but since John is at home, you can't do much.
Wait several days until John leaves. (He stays at home for 7 days and then he is gone for the next 14 days.)
Finish Janice's birthday event: buy her a dress, get a necklace and make a reservation for restaurant.
You will take her form behind, the night after the restaurant. From this point you'll be able to fuck her ass anytime you want. So next time when John is at home you can do step 352.
I'll keep my fingers crossed for Janice to give her lovely ass to you.