A breastfeeding session for a newborn lasts between 25 minutes to as long as 45 minutes.
Your newborn will stop feeding when they are full so you should continue to feed the baby by breastfeeding until the baby pulls away from the breasts.
Once the baby pulls away from the breasts they are full and then you can burp the baby to remove any possible trapped gas.
It's okay though if the baby does not burp after feeding because not all feedings give the baby gas in their stomach.
But you should try burping them after the feeding just in case.
You won't overfeed the baby and the baby should be done breastfeeding within 45 minutes.
Just like when you bottle feed a baby they may drink the whole bottle of formula and then be full and then sometimes the baby may only drink half of the bottle of formula which is okay as well.
The baby will push the nipple of the bottle away as well and refuse to take the nipple again until it's hungry.