it'll be easiest if you wait at least a week, or when the pin feathers start coming in. If you want to play it safe you could even wait two weeks!
What works really good is Exact hand feeding formula (the kind for parrots). I have had bad luck with everything else. If you dont already know how to hand raise, I would recomend doing A LOT of research. I cant say everything here, it would be pages long!
You'll need a set of syringes. 1cc, 3cc, 6cc, and on up to about 12 cc. You can either use catheter tubing to insert into the crop, or squirt the food into the throat via syringe. Some people use bent spoons too instead of syringes.
Be very gentle and point the syringe to your left side (the pigeons right side) into the esophagus, not the trachea, so he dosent aspirate. Squeeze the food out a little bit at a time, allowing him to swallow. Top off each feeding with a layer of cool water.
Youll just be feeding a little bit (2cc) at first, every 2-3 hours except for at night, when the crop needs to empty. Gradually increase the feedings and the intervals. You can feel the crop to check that you fed the right amount. It should feel full, but not tight. When it nears weaning time, start putting small seeds into the mouth, for extra nutrition and to help the bird get used to the taste and feel of the seeds.
I wish you the best of luck with your baby!