Confusing argument from GotQuestion (Calvinist) about 24 Elders I read from this link:


  A. Some people believe these twenty-four elders represent Israel, 
  but at the time of this vision, Israel as a whole nation had not yet been redeemed. 
  
  B. The elders cannot represent tribulation saints for the same reason
   not all had yet been converted at the time of John’s vision. 
  
  C. The most likely option is that the elders represent the raptured
  Church which sings songs of redemption (Revelation 5:8-10).


What made me confuse is because on point-C, I can also say :
but at the time of John’s vision, there is no raptured Church yet.

So, the question is :
Did Calvinist say (in point-C) that at the time of John’s vision there is already raptured Church?

On the other hand, 
If what Calvinist meant (in point-C) is at the time of the "End Time", 
Then why the argument in point-A and point-B use at the time of John’s vision ?
You seem to be asking how the non-occurence of certain events are said to rule out certain interpretations of Revelation 4:4 and not others. I think this confusion can be cleared up if we recognize the difference between 'historical' non-occurence and 'narrative' non-ccurence from within John's vision.

The pre-tribulation and dispensational pre-millenial perspective that the author(s) of the article on GotQuestions seem to be writing from (see the beliefs of the author, Paul Benware who is cited at the bottom of the article) fits with points A and B that you summarize above. While it is true that for a dispensationalist neither A, B, nor C have occurred in a 'historical' sense from the time of John's writing, there is a 'narrative' time and order of events that seem to undermine pre-tribulation dispensational pre-millenialism if the 24 elders refer to either the elders of Israel or Tribulation saints.

The author(s) seem to feel that Revelation 4 takes places (within the narrative of the vision) sometime before the tribulation, but after the rapture. If A were true, then the narrative would be off because Israel has not been redeemed yet within the narrative and so there would be no 24 elders, but if B were true the narrative would still be off because tribulation saints do not appear yet within the narrative. Both A and B are not possible because the author(s) believe that at the 'narrative' time of John's vision the tribulation not considered to have occurred.

The challenge then becomes discovering who the elders are if they are not either A or B. The author(s) of the article then seem to assume that while the tribulation has not occurred, end-times events have nevertheless been kicked off and saints have been raptured. It is then from these raptured saints that the 24 elders must come. The confusion arises from not understanding the radical distinction held by dispensationalists between Israel and the Church and the fact that at the time of John's 'writing' within the narrative the tribulation has not occurred (or been completed).