We started using CIO at 6 months, but there were times before that that Anna would go all night (6-10hrs) without a bottle. She actually slept 6+ hrs from 6 weeks until 4 months & then started getting up at night 2-3 times until eventually she was waking up every hour, which was why we started CIO. During the time she was waking up a million times a night was also when my PPD peaked, we moved & we switched her formula.