When letting a baby cry it out you can let the baby cry it out for 10 to 30 minutes.
Most babies are able to cry it out and get to sleep within 10 minutes of crying and usually they just stop crying and then fall asleep.
Before letting a baby cry it out make sure the baby is not hungry, needs a diaper change, or is not sick.
If the baby is okay then you can let the baby just cry themselves to sleep and they will eventually fall asleep even though it seems like they never will.
When letting your baby cry it out let the baby cry for 5 minutes then go in and check on them and gently pat the babies belly and tell them that you love them and tell them it's okay and goodnight.
Then leave the room and repeat the process of going back into the babies room and comfort them but don't pick them up.
Then extend the time you leave the room and continue going back in the room to check on them until they do fall asleep.
Babies eventually will fall asleep but it just takes time for them to comfort themselves to sleep.