The sooner you sell an option the better. Place a limit order to sell as soon as you buy it. Options trades typically have a one day settlement so the trade settles the next day of business. Most brokers require that you pay in cash. Options are not marginable.
Options are open for trading in rotation after the stocks open for trading.
There may be volatility in the first hour of trading or a market panic where prices are severely distorted. Here is one time where knowing what the options are worth will save you overpaying by up to 300 percent. The Volume column will tell you how many options are currently trading. It helps to keep track of both and check the calls against the puts to see where the buying and selling is. But don't assume the crowd is right.