If you want to go to the Grand Canyon, I agree...call ASAP. They book ahead 1 year from the month of your visit. IF you have a choice, go to the North Rim, it's relatively quiet compared to the South Rim. We've done them both, over 2 different Memorial day weekends.
For cash, and the cancellation policy is good, in a reasonable time line. Book if you think you'll be going.
Bobbi