What do you think of 1/session items? Or help me find a better way to solve this plot hook. I’m stumped

I wanted to give my players a homebrew item, but I’m having a hard time balancing it around in-game / in-universe limitations. Normally this is like 1/day, 1/encounter etc.

I was thinking of doing 1/session (once per d&d session). Is that too meta?

For specifics, this item is a tome of knowledge which will allow them to ask some # of questions (I’m thinking 2) per [some time frame]. The books knows everything its previous owners knew. I’m doing this so my players have an in game mechanic to help them find the items they need to take down the BBEG.

Alternatively, if you have a suggestion how my players can find the ‘x old artifacts’ that legend says are needed to kill the BBEG that would work too. I’m trying to have them find something to help them find the artifacts without an in game person just telling them where they all are or just having them wander into the items randomly (both of which don’t seem satisfying).