WillowTree,
Matthew 16:21 From that time on Jesus began to explain to his disciples that he must go to Jerusalem and suffer many things at the hands of the elders, chief priests and teachers of the law, and that he must be killed and on the third day be raised to life.
This seems consistent with: day 1, crucified and died, placed in the tomb; day 2, in the tomb; day 3, raises from the tomb. On the third day would be Sunday if the body was buried on Friday. Unless you want to claim that the scriptures are mistaken, you seem to be in a quandry.
From my understanding, the Roman soldiers were thinking of breaking Jesus's legs so that he would die sooner. This was because sunset was approaching and the Sabbath would begin at sundown. However, Jesus died just before sundown. This means that he died on Friday, just before sundown. Doing my own math, Friday just before sundown to Saturday just before sundown is 24 hours. Saturday evening to Sunday morning is another 12 hours. The bible is claiming that Jesus was in the tomb for 36 hours, not the 72 hours you are claiming.