According to pre-tribulation pre-millenialists, when would and will Christians be persecuted for their faith as a sign to the world?

If I understand correctly John Darby, the father of Dispensationalism sees Mat 24:9 as pertaining to the time of the disciples in Israel as well as chapter 10.

The time of the disciples' testimony is characterised by false Christs and false prophets among the Jews; persecution of those who render testimony, betraying them to the Gentiles. But there is yet something more definite with regard to those days. There would be false Christs in Israel. There would be wars, famines, pestilences, earthquakes. They were not to be troubled: the end would not be yet. These things were only a beginning of sorrows. They were principally outward things. There were other events which would bring them into greater trial, and test them more thoroughly-things more from within. The disciples should be delivered up, put to death, hated of all nations. The consequence of this among those who made profession would be that many would be offended; they would betray one another. False prophets would arise and deceive many, and, because iniquity abounded, the love of many should wax cold-a sorrowful picture. But these things would give occasion for the exercise of a faith that had been put to the proof. He who endured to the end should be saved. This concerns the sphere of testimony in particular. That which the Lord says is not absolutely limited to the testimony in Canaan; but as it is from thence the testimony goes forth, it is all connected with that land as the centre of God's ways. But, in addition to this, the gospel of the kingdom should be preached in all the world for a witness unto all nations, and then should the end come - the end of this age. Now, although heaven is the source of authority when the kingdom shall be established, Canaan and Jerusalem are its earthly centre. So that the idea of the kingdom, while extending throughout the world, turns our thoughts to the land of Israel. It is "this gospel of the kingdom" [See Footnote #67] which is here spoken of; it is not the proclamation of the union of the church with Christ, nor redemption in its fulness, as preached and taught by the apostles after the ascension, but the kingdom which was to be established on the earth, as John the Baptist, and as the Lord Himself, had proclaimed. The establishment of the universal authority of the ascended Christ should be preached in all the world to test their obedience, and to furnish those who had ears to hear with the object of faith.

Footnote 67: The gospel of the kingdom was confined to Israel in chapter 10 and here this, though no subject of the teaching, is the subject supposed up to verse 14, but there is no formal distinction made: the mission in chapter 28 is to the Gentiles; but then there is nothing of the kingdom but rather the contrary, though Christ be only risen, but all power given to Him in heaven and earth.

Matthew 24

Your question tho aimed to a specific grouping of individuals, has peaked my interest. The question of when as you have pointed out is everyday, for people in various places tho not in your locale... One hears of people being gunned down in churches, wiped out of villages and the such... But what I get from you is when will there be arnachy right? Chaos as some others would term it... Get this, that would be after Rapture... Now altho I hold to no specific denomination tho I frequented them whilst growing, I know this sort of responce would be termed pre-trib... And whilst I am not a proponent for any official wording or doctrine of any specific group I do find this consistent with the scripture... I could cite them but of course you may be well versed yourself, so here it goes my reasoning:

Not all believers are and would be ready to depart in Rapture, some are like the 5 foolish virgin's whose oil has finished (yet they are still virgins tho foolish). They will be witnesses to affirm the event of the rapture and be the ones to counter the official (And I mean governmental) explanations for the bizzare events of the rapture and everything that follows... [Mass alien abduction may be the buzzword]... and the 'aliens' [angelic manifestations of The OTHER kind] are not the other worldly sci-fi entities you were brought up on... But rather spiritual entities, manifested...

Believers who were not 'ready' tho 'left-behind' will be very aware of what occurred, and will be the ones to continue witnessing, preaching, converting those who are left here, or even born then, about the God of the Rapture... but that is on the physical side, the spiritual side of this is that the rapture will be simply the withdrawing of the Restrainer (Holy Spirit) and with him all who house him in their hearts as referenced in Thessalonians (those who accept the free gift of salvation, offered by Yeshua [Jesus Christ])...

Now when the Restrainer is removed along with the saints he inhabits, then obviously, what was being restrained will be allowed free reign and may manifest fully in our physical world... take a look at popular media to get a glimpse of what is to come (spiritual expression [zombie apocalypse]) is just one buzzword I will use to set you thinking due to the Restrainer being removed... that is when the message would be prosecuted as referenced by the scriptures u cited, when God in the Spirit form (Holy Spirit) would not daily restrain but leave man to his choices and devices, yet still faithfully accept those who would hear even in those days, and believe, confess and even be matyred in His name...

The saving grace is we still have time! Today to be specific, make that decision today, be vigilant, be (spiritually sober), be ready!..

As further encouragement; Revelation 20:5-6:- Blessed and Holy are you, if...