because of the testimony which they had maintained

One of the many challenges in understanding eschatology is gaining a sense of the timing of events. Because there are many New and Old Testament eschatological prophecies, it is challenging to keep track of all of them and how they are related to each other; this is where of the power of charting your observations come be appreciated.

The Great Tribulation is a distinctly different period of tribulation, and it appears that the Great Tribulation begins just before the fifth seal.

Jesus prophesized that the Great Tribulation (Matt 24:21; Mark 13:19-20; Luke 21:23-24) will occur when "the abomination of desolation which was spoken of through Daniel the prophet" is standing in the holy place which locates this event in the middle of Daniel's 70th week. Unlike tribulation in general, the Great Tribulation will be a time to flee (Matt 24:15-16; Mark 13:14; Luke 21:20-22)

This is one of the pieces of circumstantial evidence that the "abomination of desolation" has desecrated the Temple by the time of the fifth seal.

From Revelation: An Explication © A resource for learning how to read the Bible.