I leave my curtain open in the day and off all light except a small light at night to let baby know the night and day different. Poop once a day or once 2 days is fine. If u see poop stain, you try to tell the baby mmmmm.... mmmm... mmmm.. Soon baby will know they have to try to poop. Also sometime it can be also due to formula milk.
Newborns cannot differentiate night from day so let him sleep during the day. You can help him adjust by dimming the light at night. Is he in pain? If not it's ok, especially if you are breastfeeding.
Eileen Lau