Maybe this doesn't mean anything, but in the script, when Patricia mention the Sunday horse riding event, it is not tied to anything, there are no conditions for that dialogue to happen. So it seems logic to expect that it will happen no matter what.
Obviously, he can always limit or condition that later on (i.e. Patricia calling to cancel or not calling at all etc).
But like you I found strange the you have to be in Aiden's task route to have the event. Not being on Aiden's task route could make a little bit more sense because then it could be the alternative event to the horse riding (i.e. Aiden's 5th task). But in that case we gonna have 3 tasks in the space of 4 (real) days, maybe too much?
On a side note, the horse riding happens on Sunday, while the PD 14 is a Saturday I think. Otherwise Patricia has to call Sophia some time on PD 13 (Friday) and we skip one day.
And in the evening of PD 14 we have the museum guy event (because the museum is closed). So either it will be at end of the horse riding event (PD 14 is a sunday) or before the horse event (PD 14 is Saturday, and PD 15 sunday).
In that case (and in any case) the sentence:
can be a little ambiguous. Is he meaning also
end of day 14 or just day 14 in general?
Not that it makes a big difference, we know that it won't a sex scene. Also it depends on his concept of hot scene, once we will see his idea of hot scene for the Mayer's boy maybe we can think about something