Seems like they're preparing a new part of Time Temple.

Arn't we in the present, and that is the reason why the door to the present is open? The past door is broken, and the powerfull force brok for us to go to the fture. This door is most likely another future, since the future can be changed, over and over again. This is what happens when you play with time.

We don't have access to the past yet. We have "Present" and "Future", no past yet. I wouldn't doubt if this is actually an extension of the future, since we've only seen a small glimpe of what destruction has occured in the future. We haven't even seen what happened to the other continents and towns, and having a "Future" Temple of Time be accessible could be just what we need to see the horror.
Maybe Nexon is pulling a "Ocarina of Time" on us and they're showing us the future Maple World if none of us (Adventures / Heroes / Resistance / etc) appeared.