Options can be executed any time during the ICO. During the first day of ICO tokens are sold to option holders only, and option holders are guaranteed to be able to purchase their coins. Starting from the second day of ICO tokens are available for purchase to everybody. However, option holders still can execute their options if there are enough tokens left in the total pool.

If a person changes his mind, he can execute the option partially or not execute it at all. Let’s take the example from the article when a person bought option for 5$ and reserved 130GVT. Instead of paying remaining 95$ he can pay, for example, 47.5$ and will get 65GVT.
However, the price of the option (5$) is non-refundable. A person won’t get 2.5$ back in the previous example.