But it seems like Jesus was not in the tomb during the three hours of light on Thursday. So the only periods of light when He was in the tomb would be Friday and Saturday. He said He would be "in the heart of the earth" for three days and three nights not just that He would be dead. I think this idea is worth investigating but a few details need to be cleared up.
At 3 PM, the moment his body ceased to live, HE the Mind/Spirit that had developed within that body began HIS descent into the bowels of the earth, where he preached the Good News also to those in the world of Hadesits
It is wrong calculation as Jesus was a Jew and the Jews followed lunar calendar.
Jesus was put in the tomb after the sunset in the tomb, so the counting should be started from Saturday.
There are Christian people who believe that Jesus was put on the Cross not on Friday but sometime earlier, so there is no proof as on what day Jesus was put on the Cross.
Regards
Jesus, the reality of the Pascal Lamb was Killed between the two evenings that preceded the 15th day of the first month, whereas the Pascal Lambs were supposed to be killed between the two evenings that preceded the 14th day of the first month, and the Lamb was to be eaten in the evening and beginning of the 14th day.
Exodus 12: 6; English translation: “Then on the evening of the 14th etc.
The Hebrew” Exodus 12: 6; -beyn haarbayim, "between the two evenings."
The Jews divided the day into morning and evening: Up until mid-day, all was morning or fore-noon; after that, all was afternoon or evening. Their first evening began just after twelve o'clock, as the sun began its descent toward the horizon and continued till sunset; their second evening began at sunset and continued till night, i.e., during the whole time of twilight; between twelve o'clock, and the termination of twilight, when the Passover was to be offered.
The Lambs originally were killed between Mid-day and sunset of the thirteenth day of Nisan, [Jesus died at 3 PM, midway between 12 and 6 PM.] the lambs were supposed to be eaten in the evening of the 14th day of Nisan which was the beginning of the 24 hour day of Passover, which finished at sunset which was the beginning of the 15th day of Nisan, the first day of the seven day Festival of Unleavened Bread, which followed the 24 hour day of Passover, of which day the Lord says in Exodus 12: 14; “You must celebrate ‘
THIS DAY’ as a religious festival to remind you of what I, the Lord have done, Celebrate it (One day) for all time to come.
The Passover was to be eaten in the evening and beginning of the 14th day of the first month, when the sunset of the 14th day, the 15th day of the first month, which is the first day of the seven day Festival of Unleavened Bread began and it was on the first of the seven day Festival of Unleavened Bread , the evening and beginning of the 15th day of Nisan, that the Jews ate their Passover Lamb..