John:  The Resurrection/Rapture event involves two groups: (1) the dead in Christ rising first, and (2) the living in Christ being caught out following the rising of the first group.

This event described by Paul in 1 Corinthians 15:52 and 1 Thessalonians 4:17 is not an imminent event in the sense of “it could happen at any moment”.  Imminency is described six times in the Book of Revelation, a Jewish discourse for Jews, during the Time of Jacob’s Trouble, Daniel’s 70th week.  Jesus says He is “coming quickly”.  He is speaking to Tribulation Jews who are looking for their Messiah Yeshua.

The Resurrection/Rapture event is an “appointed time”.  It will be associated with the Feast of Pentecost.  Pentecost was only partially fulfilled in 30 A.D. when the Holy Spirit was given to believers.   The “deposit” of the Holy Spirit was a down payment which will be followed by the conclusion of the matter, the redemption of the body.  One feast fulfilled in two stages exactly as Paul described it.

Study 1 Corinthians 15:20-28.  You will notice that Paul speaks to the “three orders” of the first Resurrection which is a resurrection of righteousness “in Christ”.   These three ordered events track the three pilgrimage feasts. 

When is Pentecost?  Nobody really knows for certain.  In any year, there are at least four date guesses based on the 50-day count.  It is probably in the Spring time on a Sunday in Jerusalem.

For a detailed analysis, you may check out a book which has been published on Amazon titled: “The Day of Thy Visitation: The Time of Jacob’s Trouble”.  It covers this and other end times matters in great detail with over a thousand supporting biblical citations.  It is available in Kindle and print format.

The book suggests that the year 2019 appears as the prime candidate for this event based on a number of biblical prophecies.
 

https://www.amazon.com/Day-Thy-Visitation-Jacobs-Trouble/dp/1981076387