So, thinking about this, my only reasoning that SE has decided to place entry restrictions is this:

Their game has proven that it can't handle massive amounts of people in the instance servers so they staggered the ability to enter into them.

Basically rotate giving each data center a 3 hour window to get in.

This leads to the basic question: Why in the heck did SE decide to use instance servers for the limited time event, knowing they can't handle the massive crowds?

WHY DO THEY KEEP ADDING INSTANCED CONTENT WHEN THEY CAN'T DO IT?