When to start sleep training...?

I wish I had an answer for this, and no amount of googling can really tell one when to start. Some websites said you must start before 3 months as otherwise they'll develop bad habits (a bit late on that one, hey). Other sites said either between- 3-4 months ("Infants are developing a night sleep cycle, are more sociable, and show little separation anxiety, so they start to snooze better")
or 5-7 months: They are over their 4 month sleep regression, and not too old to develop separation anxiety.

Some websites say never to start before 4 months, and some never before 6. 

It is not only super confusing, but also such a lucrative money making business. I am sure I am not the only desperate mother out there, desperately trawling the internet for some sort of magic sleep solution. Really I am looking for an article or a book called "How to get your post colic, breast feeding on demand, non pacifier using, cosleeping, non self soothing baby to sleep in 5 minutes". Needless to say, it doesn't exist. 

I think Pi has just hit the 3-4month sleep regression. It's hard to tell sometimes, but the last two nights he has been sleeping terribly. Waking up every 10 minutes after he goes to bed, and then his usual every two hours. But the last few nights there has been lots of crying in the night too- which thankfully is unusual for him (He usually feeds and then goes back to sleep. It has meant that while he has been sleeping more and more of the night in his bedside cosleeper, last night I gave up and brought him directly into the bed (from 30cms away, to in my arms); though he still cried. 

I read forums of people complaining how their little one has gone from sleeping 7-8 hours in a row, to 2-3, or 4 hours. I think Gosh- if only I had four hours! I suppose though I never got the chance to get a bit of sleep back, and then miss it again. I have just ordered the book "healthy sleep habits, happy baby"- which I believe has all the different methods outlined. See if I can find one right for me.

I am still flip-flopping between training in two weeks (Pi will be just before 4 months, and Husband will be on holidays to help with the training), or training in two months (The start of October will put Pi at 5 1/2 months, and all our house guests over September will be gone). Right now, I am opting with later. He is still a little baby, that has only just worked out he has hands; so I am thinking that sleep training him at this stage might make him feel a bit abandoned (Just my own opinion with my own post colic baby). 

But see how my mind changes at 7pm tonight.....