LullbeeMany newborns come home with their clock upside down, sleeping soundly through daylight and wide awake at 3am. This is not a habit or a problem to discipline away. Before birth there was no daylight, and babies are born without a running circadian rhythm at all. It develops over the first several weeks, and parents can gently speed it along.
Contrast is the teacher
The clock is set by difference. If day and night look, sound, and feel identical, there is nothing to learn from. The fix is making the two halves of the day as different as possible.
Daytime: bright and alive
Naps in normal daylight, in the living room, with the household audible. Feeds with the curtains open, chat, songs, faces. Daytime sleep does not need protecting from life at this age, life is the lesson.
Nighttime: dark, dull, and low
From the chosen bedtime on, everything goes dim and boring. Low light for feeds, minimal talking, no play, straight back down. Night feeds happen in the sound and darkness of night, so the message lands, this part of the day is for nothing.
Give the halves different sounds
A clever trick is a dedicated day sound and a dedicated night sound. Something lighter and airier for naps, something deep and womb-like for nights, every single time. Within a couple of weeks the night sound alone starts announcing what time it is. Lullbee's nap shelf and womb shelf are built as exactly that pair.