Hi Lauren,
In order to arrive at the Disney Theme Parks in time for park opening each day, I would recommend being at the
bus stop at
Disney's Pop Century Resort at least 75 minutes prior to park opening time.
This should give you adequate time to wait for the next bus to your desired destination to arrive, travelling time to that Theme Park as well as enough time to get through security/bag check upon arrival at the Theme Park of your choice.
Arriving at the Theme Parks in time for park opening is a great idea which my family adopt each and every time that we visit the Walt Disney World Resort.
You will be amazed at just how many attractions you will be able to enjoy with minimal lines during the first couple of hours of the day. If you combine this with securing FastPass+ selections around lunch-time/early afternoon by which time the crowds will have increased, you will be able to accomplish so much without having to spend significant periods of time waiting in line.
Wishing you a magical trip filled with memories which will last a lifetime!
Emma