I ate a hamburger 25 hours before my gastric sleeve. Is it safe to have my surgery?

It's important to follow your surgeon’s pre-op instructions, especially regarding diet. Most surgeons require a strict pre-op diet to shrink the liver and reduce surgical risks. Eating a hamburger 25 hours before surgery could pose a risk, depending on your specific instructions.
I strongly recommend that you contact your surgeon immediately and let them know. They will assess whether it’s safe to proceed or if adjustments need to be made.

Hello, I hope you are well. Although it is preferable to follow your pre-operative diet, your surgery would not be cancelled for eating 25 hours prior. Keep in mind however, you should not have anything in your stomach at least 8 hours prior to surgery. In that case, surgery would be cancelled or at least postponed. I hope this answe was useful.

We recommend liquids only 2 days before surgery.  It helps reduce complications during and after surgery.  Your stomach should be completely empty before gastric sleeve surgery.   I hope your surgery went well with no complications.  Make sure you stick to your post operative diet and recommendations for best recovery after surgery.

Before of all, thanks for the great question. 
In cosmetic or other surgical operations, generally it is safe to eat something a day before the operation. However, you have to be careful about not eating after the surgery. It's not safe and you need to have a diet program according to the doctor's advises.