Although the question is in the title, I'm trading AMC options on NYSE, and I'm the seller of a vertical spread. Can I get assigned after the market has closed on weekdays like today? I've heard that 1:30 hours after the market has closed on Fridays it can be exercised, but today is a Thursday. So can I suddenly wake up to know that I'm at a loss?
The owner of an American style option (equities) can exercise his contract any time before expiration. It's my understanding that you have until 5:30 PM EST to do so on expiration day but I have read articles that say 5:00 PM.
Exercise of your option does not create a loss. Assuming that there isn't a pending dividend, the ITM short leg is already ITM with no time premium remaining. You have already incurred the loss. It's just not realized until assignment occurs.