Hi Melinda,
I can't think of a better way to start Christmas Day at the Walt Disney World Resort than breakfast with Mickey Mouse & Pals at
Chef Mickey's.
The absolute quickest way to get from Disney's Pop Century Resort to Disney's Contemporary Resort would be to take a cab.
If you will be using Disney's
Complimentary Resort Transportation your best bet would be to take a bus from your Resort hotel to the
Magic Kingdom Park and then from there, take a short stroll (or the
Resort Monorail) across to Disney's Contemporary Resort. You'll want to allow at least an hour for this journey which includes for time which may be spent waiting for the next bus/monorail to arrive.
In your instance, I'd recommend being at the bus stop at Disney's Pop Century hotel by no later than 8:00 AM on the day of your Advance Dining Reservation.
Wishing you a magical trip filled with memories which will last a lifetime!
Emma