We are talking about having the spike near a window that is cooling significantly at night and not right in front of the open part of a window that is letting in 35 degree air to cool your entire room - right? I have phals in the window ledge at work that have started spiking just from the cooling they get from the cold coming through the glass (windows don't open). The office temperture as a whole doesn't vary much at all 24 hours a day.
At home I currently am opening a bedroom window to cool my phals at night - it is getting down into the mid to low 30's outside - but my plants are all 3-4 feet or further from the opening in the window. The room as a whole is getting down into the mid 50's (give or take).