When is the last time/date I can sell an option contract?

Question

I am long on a few put options that expire this Friday. They are currently in the money (ie the stock price is below my strike price... *knock on wood**). I am utilizing Robinhood as the brokerage account. Assuming the option remains in the money, when is the last date/time I may sell the option? If the expiration date is 2/28, is the last time I may sell:
3:59pm EST on 2/27
or
3:59pm EST on 2/28
Or, put another way, does the option expire at the beginning or the end of the trading day?
Though Robinhood is actually very good at explaining a lot of things, this is not explained. I have attempted to contact their customer service and haven't been able to get ahold of them.

Answer 1

Equity options can be sold until the close of regular market hours so if the expiration date is 2/28, is the last time you can sell is by 4 PM EST. I doubt that you are referring to them but note that there are some European-style index options that have AM settlement on the third Friday of the month.

I would suggest that you speak to customer service because in their option agreement, Robinhood has some language to the effect of allowing them to exercise your ITM options at expiration. This statement doesn't make a lot of sense because the OCC automatically exercises all expiring ITM options at expiration so it's hard to know if it's a redundant statement or an additional in house regulation.