So I kinda have a secret hope that the rolls of Ren's next day go really bad, just to balance the luck she had for them for Day 2 o.o
Seriously XD
Anyway, since Ren unlocked it (was kinda hoping someone else would first, but whatever), ill explain how Time Compression Pseudospace works.
In this RP, you can only create one per day (Gaia sets limits for how long people fuck with time). Meaning that if you would want to use it to grind monsters you would simply need to make new monster IDs in it each time, not able to use it for anything else. If you have some other type (like the Training ID, which makes grinding Skills a % amount faster equal to your level in ID Create + 5) then you could say do that with the Compression Space. However, you cannot switch types. This means that if you were to be grinding and want to train skills in the Training one you would have to break the monster one (and the compression with it).
So there is obviously the 1/2. What this does is turn 1 Day into 2 essentially. (naturally you would need to sleep). The 1/3 turns 1 day into 3 and so on and so forth. Note though that Time Compression Pseudospace puts stress on your character. For one day its fine, you just regain stamina at a slightly slower pace and it may affect tasks or things that acquire long periods of stamina. For the second day you would get a -5 to all Rolls. Third day in one gives you another -5 and so on and so forth, as the more you stay in the compressed time-space the more stress you put on yourself (that's why its so good for training though, as it pushes you to the limit and beyond). Meaning you could potentially get 10 days in one day, but by the time you hit that 10th day you get a -50 to all rolls (it gives you a -10 instead of -5). Its not exactly easy.
Note that if you stay beyond four or more days in one and get a Fumble on a auto-resolve for grinding, I will kill your character. Plain and simple, on the reasoning that your accumulated stress caused you to screw up in a battle that let an enemy get in a powerful blow (or several blows). Getting a bad result will cause you to break the Pseudospace early. If you break it early you cannot make one for another 24 hours (meaning if you were in the evening when it broke, then you couldn't make it until next evening).
At Day 7 and beyond just getting a really bad result may cause your character to auto-die.
So while time Compression can let you do some serious power leveling for grinding, its also incredibly dangerous and can lead to character death even during grinding (which I decided that there would be no character death in under normal circumstances).
Note that the same can be said for Skill grinding attempts that have the potential to backfire. That could also kill you if you fumble after day 7 (instead of day 4, since continuously grinding skills isn't as stressful as continuously fighting monsters). (This is usually for magic users as certain kinds of magic can backfire with nasty affects if you fumble, especially darker magics, but even elemental magic has some bad backfires. Arcane magic backfiring is usually the magic just explodes in your face).