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

So, is this the door to the past? I can't remember which door we had open to begin with and we just got door to the future.
Or is this an extension of the future? I'm kinda leaning toward the latter.

I'm leaning towards more door to the future areas myself too, but yes, the first door we had opened was the door to the present, and we can be pretty sure its not that.

Edit: Yeah, I'm a idiot, the door that is "open" is the middle one, which is the present, but we never go through it, the one we enter through is the past which has a small crack in the door. Yeah.