After gingivoplasty procedure done, how long before you can eat?

Soon afterwards. It depends on the extent of the tissue removal. Usually you need to stay on liquids then soft diet for a 4-5 day period. Any wound would fare poorly if food was rubbed into it. This invites bacterial to overgrow the wound. The mouth does not have any properties that make it safer to place food into a surgical site. Laser induced wounds heal much faster than scalpel induced wounds.