In my case it is between 1 and 2 hours only in the morning
It depends upon 2 factors: quantity and quality.
About quantity, 2 users (Newbies, for example) can spend same amount of time per day (in average), for example: 2 hours per day. I don't go to they spend their time at morning, afternoon, or at night. It's their personal spare time.
About quality, how they use their 2-hours each day on the forum? This will make them become different with each other.
- Bob: spend his time to read Forum SMF User Help: Introduction; to search for answers with Forum Search, and learn additional things at Beginners & Help board. Maybe more but I stop at it as an example.
- Alice: spend her time to read and find easy (mostly shit) bounties at Bounties (Altcoins) and do nothing more.
After 2 months, Bob and Alice will grow at different levels and they will become very different. Bob will become more knowledgeable whilst Alice won't (stucked at where she begin).
When Bob become more knowledgeable, he will help the others and simultaneously learn more from the others. He will search more when want to help the others so consequently will learn more things.