So far, none of the five DAH summers dates have sold out yet, even day of. That being said, five of the seven winter dates did sell out... so this event CAN sell out. Personally, despite how the summer trend has gone so far, I think it’s risky to wait.
Note, ticket pricing is $119 in advance, $124 day of. AP discounted tickets are $89 in advance. You cannot get an AP discount on day of purchases. $89 vs $124 is a decent difference from my perspective.
FYI, DISers have reported being able to buy regular priced DAH tickets in advance, upgrade their park tickets to an AP during their stay, and then get a credit back for the DAH ticket AP discount amount (I think on a Disney gift card). You’d need to go to guest relations to do this.
Hope that helps! Good luck!