I never found out how long my kids could cry. I know we went over an hour, but not sure if we ever let them go all the way CIO. (Crying it out) I read Ferber, but it didn't resonate with me. Dr. Sears' Nighttime Parenting was much more helpful to me. My kids just don't seem to sleep the same way other kids do. My 7 yo still wakes up about once a week and wants me to walk her to the bathroom in the middle of the night.