I think every unlockable rooms in the offices section should be hidden when not unlocked.
Oh, the reason why they are not hidden is because clicking them tells you what you need to do to unlock them. I don't think it should be a secret that e.g. unlocking Mimic employee gets you access to Treasury.
Too hard.
One easy way to skip the part with crates, and lever if you got mana is to just use power jump to reach the higher door platforms. There is also a hole under the lever, so you can use power jump, or hover jump to get to it. There are also other ways depending on your Seals. I think part of the fun is coming up with more efficient ways of progressing through rooms depending on different situations.
They are fun. but there seems to be a hard cap on time limit increases in you can get in dungeons. iirc it says "capped at 85 seconds" is that the upgraded cap? I think I've only managed to complete 1 run. most of the time, I fail without even reaching the mirror room. Do you know roughly how much time people still have on the clock when they complete a level? Maybe I just suck. but most levels I feel like I always failed without even standing a chance.
All numbers you see in Player Stats are numbers that are already modified by Seals, so if you got more Seals that increase time limit, you can still add them, and see that number increase. It's important to take advantage of the extra time (the green buffer time). It's often worth getting that extra time crate and coins to pause the timer. I would need to see you play to know what you could improve at.
The thing is, you don't have to complete every run. Just make sure you don't run out of time. With days passing, you are going to start getting harder templates, but even with just playing safely you would eventually get enough points to unlock even more seals that increase time limit, extra time, give new skills. At some point you are going to have enough seals to suit your play style, and change them depending on what template you are going to be playing next.