What kind of scene are we looking at here? Is it a general description of the heavenly throne room or of a specific point in time? After careful study it seems to me that chapter 4 is describing not a specific event but rather a general view of the throne room in heaven and what goes on in it on a regular basis.
In our text, for example, it doesn't say that the throne was being set up--it simply states that "a throne was there in heaven." When John arrives on the scene, the throne is already there. Nothing new is taking place except that the prophet is now observing it. This scene looks a lot like the one in Daniel 7--but with a difference. Daniel 7 describes thrones "being set up" (Dan. 7:9). The passage depicts a specific event. But this is not the case in Revelation 4.
The general nature of this scene is even more obvious in Revelation 4:9. There it tells us that "whenever the living creatures give glory and honor and thanks to him who sits on the throne and who lives for ever and ever, the twenty-four elders fall down before him who sits on the throne, and worship Him who lives for ever and ever." The Greek grammar behind "whenever the living creatures...the twenty-four elders fall down..." indicates repetitive action, something that happens again and again and thus is not a specific time or event in either earth or heaven.
I think this is an interesting observation. We can, if we will, train ourselves to be much more observant of the Scriptures so that insights like this start popping up everywhere. It reminds me of a photography class I took. The first assignment was to photograph trees--single trees, multiple trees, a forest, branches, twigs, flowers on the trees. The teacher said, "Shoot a roll of film that features only trees in all types of places and circumstances."
At first it seemed like an impossible task. But after a while I started looking at my world in ways I had never done before. I found driftwood on the beach, stands of pines, trees losing their leaves, other trees in color, branches on the ground, etc. The point of the project was to teach me how to observe my environment and notice things I had failed to see before. Careful study of the Bible has the same effect. We become more and more aware of God's will and His ways, and as a result our lives are never the same.
Lord, give me new eyes, that I may view Your Word in ways I have never done before, ways that mirror what You see.