So it closed at $9.32 at 4pm but went to $12.55 at 7:59 pm.
Does that mean it will open at $12.55?
I thought the market closed at 4pm. Forgive the stupid question but I'm newer at this
The exchange closes at 1600, yes. However, stocks can still be traded outside the exchange, electronically, ending at 2000 and commencing at 0400 NY time.
No it doesn't mean it will open at $12.55. It can gap up or down at the break between end of aftermarket and beginning of premarket trading. And it can move up or down in the aftermarket hours which end at 2000 or in the premarket hours which begin at 0400. Not every stock will trade outside regular market hours. Some do not or usually do not. If nobody wants to trade, then there is no trade so no price and so no bar or candle for that period. Even so, they can gap up or down between trading sessions. The price depends entirely on what buyers will offer and what sellers will hold out for. Those expectations in turn will change due to news, overall market mood and direction, recent price/volume action, and more. When the market closes, life goes on and stuff changes which changes how bad buyers want to buy and how bad sellers want to sell which changes the price that the stock is sold at.
Aftermarket trading will pretty much always have high volatility, low volume and liquidity, and a high spread. For these reasons, many traders do not trade outside regular hours. Also some brokerages do not offer trading privileges outside regular hours or offer only limited hours. Because of the number of traders waiting for the opening bell, there may be a rush to buy or to sell, spiking the opening price up or down, and there can be a similar movement right at the close of regular trading.
Many day traders if not most, wait until 15 to 20 minutes after the opening bell before making a trade, because things can be pretty crazy in those first few candles and not reflect at all which way the price will go the rest of the morning.
Read this article.
https://www.investopedia.com/ask/answers/05/saleafterhours.asp