What day or date did Fudge have his birthday party on in Chapter 5?

As far as I can tell, there is nothing in the chapter that
tells us what date Fudge is born on.  We cannot really even tell what season of the year
it is.

But we can tell what day of the week the birthday
party is held on.  You can find that answer on the second page of Chapter 5.  On that
page, there is enough information to tell us that the party is held on a Saturday.  We
can tell the party is on a Saturday because Fudge and Peter's dad can't come.  The book
says that "He had a Saturday business appointment."  That implies to me that the party
is being held on a Saturday.