There's a sentimental reason for the closing date. From the interview I did w/Mario:
A: Is there any significance to what day you close? I remember you used to be open until October.
M: When my dad was still alive, we would go into October, always. He and my mother would go back and forth. She’d say it’s slow, there’s not enough business. My dad would say, well there’s still people that want lemonade and we’d go into October.
After my dad passed away, we stopped going into October. He died September 15th 1984 and that became the day. We always close on the first Sunday after the 15th of September.
Here's a link to my favorite thing I've ever written for LTH, and by the way, he died squeezing lemons:
http://lthforum.com/bb/viewtopic.php?t=15993&highlight=marios
"In pursuit of joys untasted"
from Giuseppe Verdi's La Traviata