After the tragic death of Piermario Morosini during Livorno's match against Pescara on Saturday, all matches in Italy last weekend were postponed. That meant that there were ten games to fit somewhere into an already busy schedule, so there was some question as to when they'd actually end up being played.
It turns out that the suspended matches will be played on April 24th and 25th, which are the Tuesday and Wednesday after this weekend's round of fixtures. The games to be made up include AC Milan hosting Genoa and Cesena vs. Juventus. The exact schedule is unconfirmed, but will probably be based around next weekend's fixtures, with the teams playing on Saturday or early on Sunday slotted in for Tuesday (the most obvious candidate being Udinese vs. Inter Milan) and the rest on Wednesday.
As of now, it's not clear when the Serie B matches will be replayed, but it's probably safe to assume a similar schedule, since they also have next midweek free.