It usually takes a day or two, put salt or meat tenderizer on it to reduce swelling and itch. Always works for me and my children. Hope it helps. Make it a paste and set it on top, can also use a baking soda paste too.
In about 3 or 4 days take some benadryl and this will help with the itching and swelling.
In addition to the Benadryl I would ice the area with an icepack to help the swelling and itching. He should be better in 3 or 4 days at most if he doesn't scratch the bites.