Mr. Penumbra's 24-Hour Bookstore - Post Reading

"All you need to do is find the right book at the right time.”
I think that what this quote means is that when you do something, you have to do it at the right time as well. If you are making an important decision, you can’t just wait forever: you will have lost your chance. Both the decision and the timing are important. 
In “Mr. Penumbra’s 24-Hour Bookstore”, this quote is very prominent. When Clay sneaks the logbook out of the store, he has to time it right or someone will notice. If he did it at the wrong time, it wouldn’t work.

Also, Mr. Penumbra had many different ideas on how to crack the coded codex vitae of Manutius. Because Corvina is the First Reader, Penumbra could get in trouble for his ideas. In this case, the only “right time” would be if Corvina wasn’t in charge, which was unlikely to happen. Again, if Clay had not had the idea to get Neel as a patron at the right time, Neel might have refused. Clay and Kat wouldn’t have been able to go to New York, and they wouldn’t have seen Penumbra. Furthermore, if Kat hadn’t come into the shop when Clay had the 3D model on his computer, they wouldn’t have gotten into a relationship, and Kat wouldn’t have helped Clay with the other problems. I think what this quote is saying is, “You have to know what to do, but it still won’t work if you’re not doing it at the right time.”