Le Jour ni l'Heure...

[fajrdrako]

I just found this wonderful picture of the Castle at Chinon. It has the caption "Le Jour ni l'Heure" and I don't understand the French usage there - it presumably means 'neither day nor night', or 'at dusk' - what does "l'heure" mean in this case?

(Beset by too many idioms!)