Open a stock while its exchange is trading, and if the price on the page is more than 15 minutes old we fetch a fresh one. The price line says "Updating price" while it comes in, and when it lands the price and the day's change roll to their new values in place. No reload, usually within a few seconds.
Underneath, the price says exactly one thing: "Updated now" if it was taken in the last 15 minutes, "Market closed" when the stock's exchange is not trading, and otherwise the date it was last updated.
Price alerts are checked against a fresh price every 20 minutes while the stock's exchange is trading, including markets we used to check only at the close.