This Thursday evening-Friday day is the celebration of Shavuot here.  This coming Sonday is the celebration of Pentecost in most (?) of the Christian churches around the world.  The instructions given to Moses by YHVH, God of Israel, regarding this very important appointed time pretty clearly indicate that the celebration should always be on a Sonday, just as should the first fruits of Yeshua’s/Jesus’ resurrection.  The counting of the sheaves begins a new thing for the harvesters (Lev 23:9-22 [v 16]); Sondays begin a new week, and “the day after” death and the grave and Hades/Sheol, where even Yeshua was on His last Sabbath before beginning a new thing from God by His resurrection from the dead, by which we entered the “last days” leading towards the “time of the end”, culminating in the time of judgment during the Day of YHVH, separating the true believers/the saints from the rest of humanity, by the first resurrection and rapture of all those “in Christ” — whether dead, or still alive.  This is the blessed hope of the Lord’s coming in great power and glory, and of the one new man being together and united with Him “in person”. (Jn 6:25-40; 11:23-27; 1Cor 11:23-32) 

This expectation of the believers visibly took place at that Shavuot/Pentecost “new thing” just about 2000 years ago:  the promise of the Father came to pass when the Holy Spirit came and fell upon and indwelt the Israeli Jewish disciples in the Upper Room, and then on 3000 more through the preaching of Peter to those who had gone up to Jerusalem, both from within the country, and those who had come from outside to fulfill the commandment for this “feast of YHVH”.  

I want to put something before you that I only paid attenion to a few days ago:  
The Apostle Peter quoted from the Prophet Joel about what was going on when some of the people present mocked those who were speaking in the native tongues of the crowd after YHVH had poured out His Spirit on them.  Peter said that the spiritually baptized believers were not drunk, but were experiencing what was spoken by Joel in 2:28-32 (Eng): 

‘And it shall come to pass in the last days, says God,
That I will pour out of My Spirit on all flesh;
Your sons and your daughters shall prophesy,
Your young men shall see visions,
Your old men shall dream dreams.
¹⁸ And on My menservants and on My maidservants
I will pour out My Spirit in those days;
And they shall prophesy.
¹⁹ I will show wonders in heaven above
And signs in the earth beneath:
Blood and fire and vapor of smoke.
²⁰ The sun shall be turned into darkness,
And the moon into blood,
Before the coming of the great and awesome day of the Lord.
²¹ And it shall come to pass
That whoever calls on the name of the Lord
Shall be saved.’ 

I’m sure that you have all noticed a long time ago that some of what Peter quoted began to come true that day, but the last part of what he spoke out did not; yet, by the Holy Spirit he proclaimed at Pentecost/Shavuot both elements of Joel’s prophesy.  What I just came to realize is that the prophetic period of the new thing that Shavuot/Pentecost brought in at that time, and what is written in Lev 23 about the appointed time, is that it began then to bring in the first fruits of wheat harvest (the first fruits of the resurrection as during the barley harvest), and ends with the Day of YHVH at the “second coming of Jesus Christ”.  The signs written by Joel, and quoted by Peter are signs at the end of the age (Yeshua said to preach the gospel until the end of the age, and He is with us all these days to do so), after which the main harvest of wheat and fruit has been brought in. (Mt 24:10-15, 29-31; Rev 6:12-17)  Even so, come, Lord Jesus!