When should I start to focus on the kanji?

I started self teaching a few months ago, and my Hiragana and Katakana are solid, but I haven't started to learn Kanji. Some sources I use say that you should start right away, but I've been focusing on vocabulary, listening/pronunciation, and grammar while reading reading the romaji and practicing with Hiragana and Katakana. I figured that I should try to understand more Japanese before figuring out how some Kanji--but is it important to start sooner rather than later?

As soon as you feel comfortable with. I started with kanji immediately when I started studying Japanese, because it opens the door to so much study material (lyrics, blogs, books, etc. -- it's faster and more fun when you can read them without having to check every single kanji in a dictionary). Of course, everyone has different study styles, but kanji are such a big part of the Japanese language and it will take such a long time to learn enough of them, that the sooner you start studying them the better.

My personal opinion? Start now. It IS possible to study vocabulary, grammar and kanji all at the same time. You can keep your focus on vocab and grammar, but seriously, the sooner you start learning kanji, the more you will thank yourself later.

Hint: Learning vocabulary written in kanji is a good way to learn different kind of compound readings etc. for kanji while you're also memorizing words. It'd be a pretty long and hard work to learn kanji separately from vocabulary, by trying to learn all the readings of the kanji without a word to associate it with.

Personally I have never learned kanji alone, it's just way too boring a drill. I've just learned them while I've been studying vocabulary, and I read almost as well as I speak and write.

Agreed with lemonworld.
Start right away, the sooner the better.
If you have any plans on taking your Japanese to adult levels of proficiency, most of what you read will be in Kanji.
Learning a vocab word in hiragana is ok, but when that word is actually written in Kanji 90 percent of the time,
it will be better to just learn it how you will actually see it written in Japanese.
It seems intimidating, but the more you learn, patterns start emerging, and parts will build on other parts.

I agree with the other replies. I started learning kanji from day 1. It is a big task to learn them, but if you want to be able to read proper Japanese you obviously have to, so the sooner you start the better. I have been learning the core meanings by rote. In theory I ought to recognise all the Joyo kanji by now, but in reality on any given day my success rate is only about 95 percent. This has taken me 18 months at five or ten minutes most days (just on kanji drill, I mean), with a few gaps. I'm not sure if that is good, bad or average progress!