On what occasion did Pharaoh restore the cupbearer and hang the baker?

Answer: His birthday

On the third day, Pharaoh's birthday, he held a feast for his officials, restored the chief cupbearer and hanged the chief baker.

“On the third day, which was Pharaoh’s birthday, he held a feast for all his officials, and in their presence he lifted up the heads of the chief cupbearer and the chief baker.”— Genesis 40:20 (BSB)