At the time the options are granted, there is no tax as the options are priced and granted based on the current stock price.
When the options are exercised with say a $4 strike price and a $24 stock price, you have a gain of $20 on the options, which is taxable at short term or ordinary income rates (virtually the same) and a new cost basis in the stock of $24.
Exercising an option is a purchase transaction, so the gain on the option is taxed at that time.
Any sales of the stock afterward will be short term gains for a year, LT gains after that. Assuming a sales price > $24.