You don't have to use your tickets consecutively. We often like to have a "rest" day in between our Disneyland days. It gives us time to enjoy the pool, explore anaheim, get some extra sleep and give our feet some time to rest before hitting the parks again. We like to go open to close so a rest day is usually very needed for our family. We have never had any problems taking a break in between our park days.
You have 13 days after the first day of use, or until expiration, whichever comes first. So feel free to take breaks or rest days, just be sure that you don't wait too long after your first day of use. Pay special attention to the expiration dates on the tickets, especially when traveling towards the end of the year. Usually tickets will expire completely on the 31st of December.