Because not all kids work this way. If I put my daughter (17.5 months) to bed any later, not only would she wake earlier but she would wake up in the night more

Because not all kids work this way. If I put my daughter (17.5 months) to bed any later, not only would she wake earlier but she would wake up in the night more too. I do know of another couple who have a similar system to you though; Dad works all day so they keep their boy up later and let him sleep in to get more family time.