Right away. It is a good idea to try to nurse soon after the baby is born. Keep in mind that your milk won't come in until about two to three days later. Also for the first few days, a new baby will be tired and not that hungry so they need a lot of coaxing to nurse. This is entirely normal. After a few days, they run out of their energy stores and get an appetite just when your milk comes in.
I would encourage... You to try almost right away after the birth. It might not be a particularly productive exchange, but it can be a wonderful bonding moment. Your first attempts will allow your child to take in colostrum, an enriched breast milk available to them right away. Then your milk will come in after a couple of days, right when baby needs it. Stick with it. The two of you will grow together from this.