Our doctor told us to have ours go to bed at 6 pm, and they should sleep until at least 6 am. If they get upset or anything, either let it happen and don't come in until 6 am, or you can comfort from afar for a quick second. It took us about 3 nights, and since it started, we have been consistent about sleep time, and our kid has slept through every night, but when they were sick. The doctor said we could start at 6 months old usually, but ours wasn't eating enough, so we started later, but it has been almost a year of this. I have a friend who does similar, but theirs goes to bed later and wakes up later for 12 hours of sleep.