We might not get a chance to get to Senlis until about 4:30 on a weekday afternoon, maybe 5-ish. Most churches in Paris are still open at this hour (but, in general, when *do* churches usually close in the evening? I know we missed the interior of Madeleine because we lost track of time and thought it would be open until dark...it closed at 7 pm.
I'm guessing 7 pm is a pretty common closing time for churches (Notre Dame de Paris actually closes at 6:45, I don't think I realized that).
So hopefully, if we arrive train station at 5, at the latest, we'll get to see the interior of this lovely church (I love its simplicity and the contrast with the stained glass, and the architects really express the essence of soaring Gothic).