He's better off exercising before the stock price increases due to tax reasons.

When you exercise an option that was given to you due to employment the income generated by the stock price - the exercise price is considered employment income. (therefore, he's going to be paying 40% tax say on the entire amount).

The increase in the stock price after the exercise date follows the standard capital gains rules. (e.g. gains x 1/2 x 40%)

Therefore, if he thinks that the stock price is going to go up in the near term he is going to want to exercise it earlier rather than later so he pays less tax.