The rapture is not a single event; it is a series of events - it does not all happen in an instant.
 
* The Lord Jesus descends from heaven, bringing the (souls of the) saints with Him.
 
This happens 'in like manner' as He ascended, i.e. progressively, (He could have gone up instantly, but I presume
the reason He went up progressively is so that the disciples could watch Him go and later testify that the saw Him
ascend to heaven).
 
* There is the sound of a trumpet and a shout of command.
 
A sound occupies an interval of time - otherwise all you have is a click.
 
* The dead in Christ are raised FIRST.
 
Presumably this happens as soon as as the Lord touches down. The saints are coming with him, so presumably
their bodies resurrect on arrival and their souls and bodies are reunited. The resurrection happens in response to
the command, so the sound is probably during the final phase of descent.
 
The word 'FIRST' implies an interval of time, the length of which is not explicitly stated, although there are theories
about that. The historical precedent is that the saints went into the city and appeared to many. During that time
the Lord Jesus is with us (the parousia).
 
* After that those of us who are alive are changed.
 
This happens in an instant. I presume the reason for that is there is no mingling of the old body with the new one.
 
* Then we are all caught up to a meeting in the air.
 
I don't know whether there is any interval between us being changed and all being caught up.
 
*Thus we shall always be with the Lord!