There’s not an exact time that we can recommend, as all babies are unique and it will depend on how tired baby was, how much sleep they got that day, etc. Ou recommendation is to be sure baby falls fully asleep. You can also try working on your bedtime routine if baby is waking up fussy—white noise and dim the lights 20 min before bedtime. bath time, etc.
The age of your baby might determine what kind of sleep-training method you choose, though. You could try a gentle shush-pat technique with a five-month-old, but you’ll likely have to leave a one-year-old in the crib as they protest (cry or scream) about the new bedtime arrangement. Don’t attempt a formal sleep-training method before four months, until your baby is able to go longer in between feeds and their circadian rhythm starts to develop. (Many babies this age still feed in the night—contrary to popular thinking, sleep training isn’t synonymous with night weaning.) Dickinson says that many four-month-old babies are biologically able to go through the night without a feed, but that doesn’t mean you shouldn’t respond and feed them if other methods of calming them aren’t working. Since every situation is different, we recommend checking with your doctor before withholding your baby’s night-time feeds.
"My 3-month-old doesn't sleep through the night, and it's fine with me. I keep her in her crib or a bassinet until her 3 a.m. feeding, and then she joins my husband and me until we get up for work. She won't go in her crib unless she's already asleep, usually from nursing and rocking, but she'll fall asleep in her bassinet beside our bed. She's happy and we're happy, and even if it goes against the wisdom of the experts, it's working for us."
That said, sleep training isn’t a must-do for everyone, and many families who skip sleep training go on to have a child who learns to sleep through the night on her own. “It’s your family and your child, and I think there’s a misconception that pediatricians will force sleep training on your family, when that’s not the case,” Gold says. Experts emphasize that the best approach to sleep training is the one that fits your family.
But when he was about three-and-a-half months old, the routine fell apart. “I would feed him, but he wouldn’t be asleep at the end of the feed,” recalls Welk. “I would rock him until he fell asleep and put him down, and then he would wake up 30 minutes later and I would do it all over again.” Desperate for some rest, Welk brought Greyson into bed with her, but then she ended up just lying still, holding a pacifier in his mouth all night long. “I didn’t know anything about sleep,” says Welk. “I didn’t know you couldn’t just rock them to sleep and then put them down.”