After surgery, your rabbit will need some special care until he/she is fully recovered.
Females take longer than males to recover from surgery. Often males start to eat the same night, but females may go nearly 24 hours without wanting to eat. It is important that your rabbit does eat some by the next morning, so "baby" her with little tiny pieces of Red Delicious apple, her favorite wet, cold greens, or hay. Replace the greens and fruit with fresh ones if not eaten within two hours. Also bring your bunny's water bottle over to her, so she is tempted to drink.
If your bunny is a male, by the next day he'll be almost back to normal. With females, it can take nearly a week, but by the next day, she should be eating at least some. Keeping the food fresh will be a big help.
Remember to call your rabbit veterinarian if your rabbit does not eat anything by the next day.