This visit occurs on the same day as the duel between Lagron and La Tour d'Azyr ("They fought this morning …", Chapter 3.VI).

Le Chapelier states that Faussigny's threat to "fall on these scoundrels, sword in hand" occurred "yesterday".  Carlyle, in The French Revolution, tells us (Book 2 Chapter III Part 3) that the Moniteur reported this utterance in the session of August 21.  Clearly, though, either Carlyle or the Moniteur is in error, for if the statement was on the 21st then Lagron met his demise on the 22nd—a Sunday, and we know that M. le Marquis de La Tour d'Azyr did not fight on Sunday.  Undoubtedly Carlyle is mistakenly quoting the Moniteur's edition of August 21, reporting the session of August 20, placing the duel on Saturday August 21.

Two potential supplemental clues prove unhelpful here.  First, Danton mentions that the King has given passage across France to Austrian troops.  This event occurred in July, and so doesn't help fix dates in August.  Secondly, André-Louis has already heard of the duel between Lameth and the Duc de Castries.  But he must have done so through a time machine, since this duel did not take place until the following November (see again Carlyle).