You must hold the stock at least one full year to qualify for the long-term capital gains rates. This is extremely important and I encourage you to make absolutely sure by holding the stock one-year and a day at least. The tax on a long-term capital gain is currently 15% if you are in the 25% income tax bracket or higher and just 5% if you are in the 15% or lower tax bracket.
As you will see, qualifying for the long-term rates is important.

Short-term Capital Gains

If you hold a stock less than one year before selling it, the IRS classifies the sale as a short-term capital gain and taxes the profit as ordinary income. This means you could pay 25% or much higher of your profit in taxes. Unless there is a compelling reason, hold on to the stock long enough to qualify for the long-term capital gains rates.