When Does a Baby's Napping Begin to Normalize?

My 18 1/2 week old baby sleeps great at night. He doesn't sleep all the way through, but he only wakes up for hunger like once in the early morning. I'm ok with that. He's hard to get to sleep, not as ok with that, but once he gets to sleep he's great. The problem is that during the day, he rarely sleeps longer than 30 minutes at a time. Should I leave him in his bed to see if he'll get back to sleep? He rarely wakes up crying, he seems happy. Is this normal? I read that irregular napping messes with a baby's ability to fall asleep at night. Does that ring true? It seems like every parenting has some strong bias and agenda, and all contradict. So, I'm asking for your experiences basically because I'm tired of parenting books. Any one else feel that same way about parenting books? (Bonus question)

Suggestion:

That sounds exactly like my first! My third is a lot like that too. I think it is normal for some babies to catnap during the day. It's not typical, and most moms you talk to will tell you it's wrong. I've been there too, and I remember that there's not much you can do about it. Get a sling so you can get some stuff done while keeping him happy. Just keep putting him to sleep gently. Eventually he will learn. With my daughter, it took years, but now she's a great sleeper.

Of course, we did the whole CIO thing at 10 months. What a huge mistake that was! At first it was great, but it was more work in the long run. If I had taught her to sleep gently, she would have slept on her own much earlier.