Aren't first communions usually in April or May, though? I was raised Catholic and I made mine on the 1st of April.
The screenplay states it's Autumn at the beginning, and the first scene of Anthony's party was filmed in the first days of October. You see people in their shorts and some even swimming so it definitely couldn't have been any later. Even in early October, the temperatures at Lake Tahoe are low, so the weather during that first scene would have been an exception.
In any case, FFC could practically do whatever he want at the time of Part II. If he wanted to start filming in May he would have, but he didn't.
