As soon as she invite. There is an immediate dik check and a check for that Jill lewd scene you are mentioning Then right after that as you see Quinn walk passed behind Jill another check kick in to see if you are not on Jills path that is an instant Quinn reject.
Yeah, I know, for some reason there are DIK checks all over Jills path despite you not really being able to swing back and forth between Affinity.Theres also ruined presentation checks for some reason.
But the big one comes when he goes to throw pebbles at her window if you're a DIK she claims something feels off and you don't get the lewd. But after this, the game starts looking for Ep7_Jill_Lewd so this is the point you exit the Jill path... but hey that's not what was being discussed it was more - it was more replying to the " You can't be on Jill's path without the dinner " which obviously is true... i was just saying it goes back a bit further than that.