I found a page that says the following about European-style options (in the context of weekly and end-of-month options for S&P 500 futures):
European-style options can be exercised only on the option’s expiration day.
This suggests to me that if a European-style option expires on a Friday at 4 pm, then a holder of that option could not exercise it before Friday, but could exercise it any time on Friday before 4 pm.
I have seen other pages suggesting that European-style options cannot be exercised at all before expiration. Is that the case, or are there certain European-style options that can be exercised at any time on the day of expiration?