Thankyou for suggesting Josephus. This is what he writes concerning the waving of the sheaf of firstfruits:
Josephus: Antiquities of the Jews: Book III, chapter 10: section 5.
- In the month of Xanthicus, which is by us called Nisan, and is the beginning of our year, on THE FOURTEENTH DAY OF THE LUNAR MONTH, when the sun is in Aries, (for in this month it was that we were delivered from bondage under the Egyptians,) the law ordained that we should every year slay that sacrifice which I before told you we slew when we came out of Egypt, and which WAS CALLED THE PASSOVER…
The FEAST of UNLEAVENED BREAD succeeds that of the passover, and falls on THE FIFTEENTH DAY OF THE MONTH, and continues seven days, wherein they feed on unleavened bread…
BUT ON THE SECOND DAY OF UNLEAVENED BREAD, WHICH IS THE SIXTEENTH DAY OF THE MONTH, they first partake of the fruits of the earth, for before that day they do not touch them. And while they suppose it proper to honor God, from whom they obtain this plentiful provision, in the first place, THEY OFFER THE FIRST-FRUITS OF THEIR BARLEY,…
…and that in the manner following: They take a handful of the ears, and dry them, then beat them small, and purge the barley from the bran; they then bring one tenth deal to the altar, to God; and, casting one handful of it upon the fire, they leave the rest for the use of the priest. And after this it is that they may publicly or privately reap their harvest. THEY ALSO AT THIS PARTICIPATION OF THE FIRST-FRUITS OF THE EARTH, SACRIFICE A LAMB, as a burnt-offering to God.
Thus, if our Lord Jesus Christ was crucified on Passover on Friday, then as Friday was ending at sunset, the 15h day of the month was approaching. This would be the first day of the feast of unleavened bread, which is a Sabbath holy day, and it would also be a weekly Sabbath day. The 15th would end on Saturday at sunset. The 16th day of the month would then begin, but the morning after the aforementioned Sabbath would not begin until after daybreak on Sunday morning. So Jesus Christ rose from the dead shortly before the waving of sheaf of firstfruits on the 16th day of Nisan according to Josephus and the gospel accounts.