Babywise suggests there are a few "normal" cry periods which include:
- just before a feeding
- when baby is put down for a nap
- during the late afternooon/early evening period
The duration of crying is set by the parents level of comfort. Personally, I chose 10 minutes to start with. I will swaddle Boston (we now use Baby Merlin's Magic Sleepsuit since he outgrew the Miracle Blanket), then lay him in his crib. I have a Baby Einstein crib soother that I put on (it stays on for 10 minutes, then slowly fades out) and I let him cry or whine himself to sleep. If he is still crying after 10 minutes, I pick him up, and hold him to my chest until he calms down, at which point I try again. I almost never make it to the 10 minute point, he usually falls asleep in under 3 minutes. If your baby is truly tired, the crying should not last long.
At night I do CIO differently. He is currently making a transition from eating twice a night, to eating once a night, so I do one longer CIO period. He wakes around 1230 to CIO and I let it go on for about 20 minutes. Sometimes he is asleep in 5, sometimes it takes the whole 20 minutes. Other moms who have done it this way during a transition tell me it usually lasts a week.
Once your baby is a few months old (around 2 months, maybe earlier) you will be able to distinguish your baby's cries. One will mean they are hungry, cold, bored, etc. This is a useful tool especially for night waking. If they are just crying without needing anything, it's fine to let them cry and get themselves back to sleep.
The following explanation is from BabyCenter:
You can find the rest of the article on CIO here, which includes step by step instructions on how to give CIO a try: Sleep Training: Cry it out methods
What is the "cry it out" method?People often think this method of sleep training involves leaving babies alone to cry for as long as it takes before they fall asleep. But "cry it out" (CIO) simply refers to any sleep training approach – and there are many – that says it's okay to let a baby cry for a specified period of time (often a very short period of time) before offering comfort.
In his 1985 book Solve Your Child's Sleep Problems (revised and expanded in 2006), pediatrician Richard Ferber presented one method of getting children to sleep that has become virtually synonymous with CIO – so much so that you'll hear parents refer to any CIO method as "Ferberizing."
Ferber himself never uses the term "cry it out." And he's only one of a number of sleep experts who say that crying – while not the goal – is for some children an unavoidable part of sleep training.