How do i know if my sinus perforation from upper tooth extraction is healing? how long does it take to fully heal?

It could take up to two months to fully heal. Make sure no root tip or fragment is left in sinus. Have x-ray taken for conformation. When you feel that no air is coming out of your nose, than your on your way to healing.

Weeks to months. Post-surgical care is part of your overall surgical procedure. The practitioner hat knows yo best should be asked your question. And he/she should be monitoring you until appropriately healed.