You'd buy it at the current ask price, which is $49.99 as I'm typing this. You'd need to go to the "After-market hours" area of your online brokerage and enter an order.

Now do I recommend buying Twitter, especially at a 30% after hours increase? No way.

So for example on July 29 2014 TWTR closed at 38.59 and now the after-hour price is 52.20. So, can I buy TWTR right now at 5 PM? And if I can, would it be at the price of 38.59 or 52.20?