Ask HN: What is the acceptable timeline to look up a solution?

As I attempt to work through the teachyourselfcs.com curriculumn, I am trying to find how long is too long to spend on a problem. Now remember, I am a beginner so the knowledge base is being built. I have spent a long time on the problems in SICP and feel it is slowing down my overall growth.

What is an efficient timeline of when to give-in and look up a solution?