When your baby doesn't need it in order to sleep well at night. Some babies don't need it at all, they actually sleep better without it as it disturbes their sleep cycles and they keep waking more often because of it. And some babies need it long into 7 or even 8 month of life. Just depends on your baby, really.
If your lo can sleep until morning and you feel like he or she doesn't need it to go through the night, drop it and see what happens. You can always go back to it if you think it was helping your lo sleep longer.
