I'm confused - your saying the notes with numbers on them are a code, and once you understand it you can find a hint in the highlighted number? How does a player with no previous experience in this cypher method decode it?
Edit: So after some googling, I learned about something called the Polybius cypher, which essentially assigns double digit numbers from 1-5 to letters in a system like 11=A, 12=B, 21=F etc. I decoded one message using that cypher to be "five Matthew", which obviously means minute hand at 5. Sorry if I come across like a highly critical ass here, but my point about puzzles not requiring outside knowledge is that outside of someone who has studied Cryptology before and actually heard of this cypher, there is no way I can fathom a player approaching, understanding and solving this puzzle. It's not so much a solution to work out as it is just a knowledge test - if you know this method, it's easy, if you don't, it's impossible. It would be like presenting a puzzle that consists of 5x5 to someone who has never heard of multiplication, they would have no idea what to do. If other comments here hadn't eluded to cryptology, I could have stared at those notes forever and never understood them, simply because there is nothing about a series of double digit numbers that makes my brain go "wait, what if 13 means C?"