Question: This scenario, based on fact, happened last month and can happen to anyone so there are some basic lessons to be learned: On Friday, the Weekly SPY options expired with SPY's closing price of 115.71. I was short 100*116/117 Call Verticals that should have gone out worthless. Instead, I was assigned 100 OCT07 Weekly 116 SPY Calls. On Monday, I was short 10,000 shares of SPY Stock.
Lessons: 1.) Trading Hours: 8:30 a.m. to 3:15 p.m. Options exchanges have a cut-off time of 4:30 pm, Central Time, for receiving an exercise notice. However, most brokerage firms have an earlier cut-off time that should be determined in advance since it may affect when you receive delivery of the stock.