Hi missingsleep. I started at around 4 or 5 months but with making sure the daytime naps worked well, and we did cc at night when he was about 10 months - ie, well after he no longer needed a night-time feed.
I'm afraid I turned a bit SWMNBN - wake at 7am, naps at 9am, 12ish and for half an hour or so at 4pm. Regular proper sleep was the only way I could stop him crying constantly during the day (I'd had a rather trying time before that.) I'd make sure he was fed, dry and comfortable, put him in the cot awake, maybe sing a song, stick this musical thing on. He'd cry for about 10 minutes, at first I'd check him a few times in those 10 minutes, and then he'd go to sleep by himself. After a month or so, or possibly less (I can't really remember) he'd go to sleep by himself without the crying. He was one of those babies that cried a lot until I got the sleep thing sorted, and I have to say, after that, he became really happy and easy to look after.
Once I'd eased him off feeding in the night, (I stopped breast feeding at 6 months) and at about 8 months slowly started watering down his nighttime feeds until I knew he was't waking for food. Then I stopped giving anything just a cuddle, then he'd go back to sleep. But then at about 10 months, he was still waking religiously for a cuddle and a bit of attention (ie, out of habit, he's never been a cuddly or clingy child) so we did controlled crying. The first night, he cried for about an hour before he went back to sleep, I went in and checked after 2 mins, then 3, then 4 and so on. the second night he slept through and has been a really good sleeper ever since, and a lovely confident boy. So it's the one bit of SWMNBN that I swear by. There may be people on here that disagree with this but I can only tell you my experience. I did read a few other books on the subject too, one was a fairly 80s ish american book I wish I could remember the name of, which talked through all the reasons you put off controlled crying, and talks you through whether it's for you or not. Incidentally, on the first night I sent DS to sleep downstairs cos I know he's non too patient and needed to go to work the next day.
Oh dear this is a bit long... but it really worked for us, so I tend to be a bit evangelical.