3 days

I still lean towards the Friday crucifixion. The red heifer might give us a clue.

Num 19:11 He that toucheth the dead body of any man shall be unclean seven days.
Num 19:12 He shall purify himself with it on the third day, and on the seventh day he shall be clean: but if he purify not himself the third day, then the seventh day he shall not be clean.

So lets say you touched a dead body. That day you were unclean (didnt matter what time of day). Then there was the next day (Day 2). Then ON THE THIRD DAY, you were purified. not after the third day (ie on the forth day).

I agree with Rene's argument, that he died on Friday as our Passover, remained in the grave on Saturday(rested on the Sabbath), and rose to life on Sunday (The firstfruits).

In Matthew 12:40 it states that Christ would be in the heart of the earth 3 days and 3 nights. How can Christ be in the grave 3 nights if he was crucified on Friday?

“Three Days and Three Nights.”—(B. F.)—If Jesus “rose again the third day according to the Scriptures,” as is testified (1 Cor. 15:4), he could not have been “three days and three nights” in the grave in the sense of three times twenty-four hours. The question is, in what sense could he be “three days and three nights in the heart of the earth,” that would allow of his rising the third day? We are bound to find such a sense, for it is certain the Lord did not stultify the facts when he said he would be three days and three nights in the grave. To find this sense, we must remember that the Hebrew mode (which was the mode governing Christ’s words), reckoned a day to consist of an evening and a morning (e.g. “The evening and the morning were the first day”); and any fraction of a day stood for that whole day as consisting of evening and morning, or darkness and daylight. Thus, in recording the transfiguration, while Matthew and Mark say it occurred “six days” after a certain saying, Luke says it was “about an eight days” (9:29). Luke counted the day of the saying and the day of the transfiguration, which only came in as fractions, while Matthew and Mark counted only the clear days between. Both ways of reckoning were right when understood. Now Jesus expired about three o’clock in the afternoon of the Jewish Saturday. In reckoning the time he was in the grave, we must count from the time of his death; for to die is to have gone to the grave in the serious sense. He died in daylight and was buried in daylight, for the women “beheld” where he was laid. (Mark 15:47; Luke 23:55). Therefore the day of his death is to be reckoned, and with it the previous night as part of the day; for the Jewish day is “evening and morning,” darkness and light make one day. The day of his death (the Jewish Saturday) was therefore the first of the three days and three nights. The Jewish Sabbath, till sundown, was the second of the three days and the three nights; Jesus rose on the morning of the Jewish Monday—(speaking in Gentile dialect so as to be understood). Consequently, he rose the “third day;” the darkness preceding the Monday morning was the third of the three nights, and the light of Monday morning the third of the three days. This mode of understanding the matter harmonises the two apparently conflicting statements that Jesus rose on the third day, and yet was three days and three nights in the grave.

1882 Christadelphian: Volume 19. 2001 (electronic ed.) (221–222). Birmingham: Christadelphian Magazine & Publishing Association.