Market Hours

That six and a half hour window is when the bulk of trading happens and when quoted prices are steadiest, because the largest number of buyers and sellers are present at once. The New York Stock Exchange and Nasdaq keep the same schedule as each other.

Orders placed outside it do not vanish. An order entered at 9pm on a Sunday sits in the broker's queue and goes to work at the open. What it fills at is a separate question, because the price at the open is set by everything that piled up overnight rather than by where the stock closed on Friday.

The market also shuts for around nine holidays a year and closes early on a handful of days, typically at 1:00pm on the afternoon before or after one of them. Exchanges publish that calendar well in advance, and it matters mostly for settlement timing rather than for anything a long-term holder does.