You can't imagine the evenings we had discussing this very topic, when we first started to sketch out the different "lessons", one of the thing we could never definitely figure out is the aspect of recording time. There's physical-limit time, for example, unless an instance finds a way to automate this, carefully drawn tally-marks might be a way to communicate how much can be done in an instantiation of the room. If I find a piece of paper blacked out in careful tally marks, I know that time allowed can be quite long, but you'd need two papers identical to ensure that each iteration is of a similar length. It might be that not all timelines are as long.
I was wondering how one could test if "objective" time exists in a measurable fashion, and had an idea for measuring time that I think is fairly novel: Clockwork origami!
Using pencils as axles and folded stars as gears, given near infinite time, I could (optimistically) fashion a small timer that should maintain its state between intervals while it's sitting inside the desk, assuming objects don't get shifted around "in between" iterations. The real difficulty, I imagine, is figuring out a power source. Harness gravity using paper twine wrapped around a pencil, with a weight on the end? Desk is probably too shallow for that, but then again it can fit people inside it... Wooden spring made from thin slivers of pencil? How I'd slice a pencil using just my fingers and my teeth, I don't know... Maybe an "hourglass" consisting of a paper sieve and graphite dust?
The limitations of the room have really made me think in weird directions. Once again, great job.