Facino returned "two days after" the battle, and at a supper "the following night" (therefore the 14th) the Duke says that the Requiem will be Wednesday [Chapter 2.IX].

As an aside, this incident provides near-certain proof to the discerning historian that Tom Sawyer, well-known adventure fan, was intimately acquainted with the story of Bellarion Fortunato.  For from what other source would he have "matured the conceit" (as Bellarion would say) of interrupting his own funeral?