Do mainstream believers believe there was a large interval of time that elapsed between the fall of angels and God speaking creating the universe?

To answer your question as asked would portend that one could read the thoughts of every Christian.

I cannot do that, but what I can do is give you the Scriptures which cover the subject and let you draw your own conclusions./

Rev 12:3 & 4 KJV

3.  And there appeared another wonder in heaven; and behold a great red dragon,
having seven heads and ten horns, and seven crowns upon his heads.

4  And his tail drew the third part of the stars of heaven, and did cast them
to the earth: and the dragon stood before the woman which was ready to
be delivered, for to devour her child as soon as it was born. 

Rev_12:7 KJV

And there was war in heaven: Michael and his angels fought against the  dragon; and
he dragon fought and his angels, 

Luk_10:18 KJV

And he said unto them, I beheld Satan as lightning fall from heaven. 

Isa_14:12 KJV

How art thou fallen from heaven, O Lucifer, son of the morning! how art thou cut
down to the ground, which didst weaken the nations! 

The only clues I find in the Bible are that Isaiah said He was cut down to the ground, and that Satan was in the garden to tempt Eve.

You can draw your own conclusion as to whether or not Isaiah's statement indicates that the Earth was already formed or not

All Christians can glean from Scripture is that Lucifer was an angel, got proud, opposed God, and was cast out for it. There is simply no data to say anything about the when, where, or why of those events.

Even what was stated above is only a tangential case at best. The entire "Lucifer falling out of heaven" narrative is not one that is explicit in Scripture. Indeed, the three closest references are:

• Ezekiel 28

“You were the signet of perfection,[a] full of wisdom and perfect in beauty. 13 You were in Eden, the garden of God; every precious stone was your covering, sardius, topaz, and diamond, beryl, onyx, and jasper, sapphire,[b] emerald, and carbuncle; and crafted in gold were your settings and your engravings.[c] On the day that you were created they were prepared. 14 You were an anointed guardian cherub. I placed you;[d] you were on the holy mountain of God; in the midst of the stones of fire you walked. 15 You were blameless in your ways from the day you were created, till unrighteousness was found in you. 16 In the abundance of your trade you were filled with violence in your midst, and you sinned; so I cast you as a profane thing from the mountain of God, and I destroyed you,[e] O guardian cherub, from the midst of the stones of fire. 17 Your heart was proud because of your beauty; you corrupted your wisdom for the sake of your splendor. I cast you to the ground; I exposed you before kings, to feast their eyes on you. 18 By the multitude of your iniquities, in the unrighteousness of your trade you profaned your sanctuaries; so I brought fire out from your midst; it consumed you, and I turned you to ashes on the earth in the sight of all who saw you. 19 All who know you among the peoples are appalled at you; you have come to a dreadful end and shall be no more forever.”

Isaiah 14:

“How you are fallen from heaven, O Day Star, son of Dawn! How you are cut down to the ground, you who laid the nations low! 13 You said in your heart, ‘I will ascend to heaven; above the stars of God I will set my throne on high; I will sit on the mount of assembly in the far reaches of the north;[c] 14 I will ascend above the heights of the clouds; I will make myself like the Most High.’ 15 But you are brought down to Sheol, to the far reaches of the pit.

Luke 10:

17 The seventy-two returned with joy and said, “Lord, even the demons submit to us in your name.” 18 He replied, “I saw Satan fall like lightning from heaven. 19 I have given you authority to trample on snakes and scorpions and to overcome all the power of the enemy; nothing will harm you. 20 However, do not rejoice that the spirits submit to you, but rejoice that your names are written in heaven.

Of the two in the Old Testament, these are actually prophecies directed against the King of Tyre - although many for historical reasons see an allusion to Satan in this. The last one, in the NT, explicitly references Satan, but this appears to be a present day thing, not related to the Fall from Heaven at all.

So, where do we get the narrative? John Milton's Paradise Lost is the most famous telling of the narrative, but the origin of the story is unknown.

As to the timing involved, there is simply no data on which to make any claim in one direction or another. Many believe that all of this occurred before the Creation of Man, since the Serpent in the Garden clearly wanted man to fall - but beyond that, much in the same way physicists can only speculate about existence a few billionths of a second after the Big Bang, there is simply no data, no framework, and no information to say any more.