The Nazgul looks pretty peeved about the smoke from his steed's severed neck getting in his invisa-face. Like he's just throwing up his hands in a gesture of "Really? Really? How am I supposed to smite with all this smoke in the way?"
That, combined with the hobbit soon to stab him in the leg, makes a strong argument for the Battle of the Pelennor Fields taking place on his calendar's (would he use one from Angmar, or one from Mordor, if the two are different?) equivalent of a Monday.