You don’t have to follow it but you should. I get a lot of emails from people who take the time to read the P90X workout schedule but decide not to follow it. This kind of baffles me. Usually, the email I get is from somebody who is just grabbing whatever disc is available and they wonder why they’re not seeing results. In this case though you really need to follow the P90X workout schedule through your first round of P90X.
The program is put together in a way to challenge you from head to toe. Each phase is designed to work specific muscles over the 90 days. How are you going to know what you can get out of P90X if you’re not following it? Do yourself a favor and complete your first round of P90X the way its designed to be done in the P90X workout schedule. Feel free to move onto hybrid programs when you’re done.