(1) For right now, FinancialData[“NASDAQ:AAPL”] isn’t working because of issues with Yahoo’s Financial Service. You can see more about this on the forum: Get FinancialData price history?
(2) If you re-evaluate FinancialData yourself, you’ll see that it doesn’t change. FinancialData probably updates itself once every 15 minutes or so depending on the query. It depends a lot based on what service you are using, what they can legally give you, and what they can afford to give you.