QUICK BIBLICAL SYNOPSIS OF THE MATTER:
The Bible says that Jesus would spend 3 full nights in the grave and ON the third day (not AFTER three full days) that he would rise from the dead (Matt. 16:21, 17:23, 20:19; Luke 9:22, 13:22, 18:33, 24:7,24:46; Acts 10:40; 1 Corin. 15:4).
The Bible also says that Jesus rose early ON the first day of the week (our Sunday) (Mark 16:9). The math from there is rather simple.
The ancient Jewish day ended at sundown (about our 6 PM). Our days go from midnight to midnight. Their days went from 6 PM to 6 PM.
THEREFORE - counting back from "early on the first day of the week" to "just before sunrise on Sunday" - this is what you get: Thursday afternoon at 3 PM Jesus dies (the 9th hour). Thursday night is one night in grave. Friday night is 2 nights in grave. Saturday night is third night in grave. Early on Sunday morning thus becomes ON the third day and AFTER three nights in the tomb.
From Thursday night to Friday night is one day. From Friday night to Saturday night is two days. Early Sunday morning is ON the third day - all of this is exactly as the Bible describes it. (Matt. 16:21, 17:23, 20:19; Luke 9:22, 13:22, 18:33, 24:7,24:46; Acts 10:40; 1 Corin. 15:4).
The math from the Bible is plain, clear, and easy to discern. Jesus was crucified on Thursday and was raised early ON Sunday. There's no other way to figure it when you let the Bible speak for itself. 2+2=4.