It is typically recommended that babies can be laid down within 30 minutes, but there are many risks associated with doing so.
Babies who are fed an incomplete milk-dependant diet (breastfeeding or formula) should not be put to bed for naps or nighttime sleep until they have finished feeding. The longer baby has his full tummy the better off he'll be in both growth and energy levels, even if it means taking baby's last feeding to bed.