"Then Esther told them to reply to Mordecai, 'Go, assemble all the Jews who are found in Susa, and fast for me; do not eat or drink for three days, night or day. I and my maidens also will fast in the same way. And thus I will go in to the king, which is not according to the law; and if I perish, I perish.' So Mordecai went away and did just as Esther had commanded him." Esther 4:15-17
Esther asked the Jews to fast with and for her for three days—night and day. These were not literal 24-hour days, or even literal 12-hour nights and days. How do we know? The very first verse of the very next chapter reads, "Now it came about on the third day that Esther put on her royal robes and stood in the inner court of the king's palace..."
In Acts 10, around 3:00PM, Cornelius saw in a vision an angel of God coming to him (v.3). He was instructed to send men to Joppa and call for Peter. "When the angel who was speaking to him had left, he summoned two of his servants and a devout soldier of those who were his personal attendants, and after he had explained everything to them, he sent them to Joppa. On the next day, as they were on their way and approaching the city, Peter went up on the housetop about the sixth hour to pray" (vv.7-9). While Peter prayed, the men knocked at his door when his vision ended (v.17). This is one day after Cornelius received his vision.
Peter invited the men in and "gave them lodging. And on the next day he got up and went away with them, and some of the brethren from Joppa accompanied him" (v.23). This is now the second day after Cornelius received his vision.
"On the following day he entered Caesarea. Now Cornelius was waiting for them and had called together his relatives and close friends" (v.24). This is the third day after Cornelius received his vision.
When Cornelius talks to Peter, what does he say?
"Four days ago to this hour, I was praying in my house during the ninth hour; and behold, a man stood before me in shining garments" (v.30). When we reckon the time by the concept of zero, which was foreign to their minds, we calculate three days "to [the] hour." Yet, Cornelius said, "Four days ago." How could he say it was four days when it was literally only three days? Because of Hebrew idiom; because they reckoned time by the concept of inclusion. Part of a day was equal to a whole day.
When we look at the crucifixion and resurrection of Jesus, we must understand this fact! Just as Esther's three days and nights were not literally three full 12-hour days and 12-hour nights of literal 24-hour days, and just as Cornelius' four days were not literally four full 12-hour days and 12-hour nights of literal 24-hours, so too was Jesus' "three days and three nights" not literally three full 12-hour days and 12-hour nights of literal 24-hour days.