Revelation 11:2,3 shows the time period of the "two witnesses" is during the 3 1/2 years of the great tribulation.
Verse 4 is similar to the prophecy in Zechariah chapter 4, where two specific people, High Priest Joshua and Governor Zerubbabel, are mentioned. Those two worked during a time of cleansing of worship on earth. They did not stand for a "class" of people. They were two specific people with specific jobs.
Verses 5 and 6 talk about the "two witnesses" doing work like Moses and Elijah that involved announcing plagues. (A lot of Revelation is talking about plagues on false worship and kingdoms in opposition to God.)
The transfiguration in the gospels pictured Jesus in kingdom power figuratively talking to Moses and Elijah. When the apostles asked Jesus about Elijah afterwards, Jesus said John the Baptist was like an "Elijah", showing that a specific person can be like "Elijah" or "Moses". The Revelation chapter 11 account was written after the time of John the Baptist, and the time of fulfillment as shown by the context is prior to the coming resurrection, so the Elijah-like and Moses-like actions of the "two witnesses" don't mean that Elijah and Moses are literally the witnesses of Revelation 11, because they are still sleeping in death.
The context of Revelation chapter 11 shows that the "two witnesses" are two specific literal people who also happen to be anointed, so they couldn't be Elijah or Enoch or Moses or anyone else from before the time Jesus walked the earth. Verse 11 shows that they are anointed to be part of the 144,000, because they are among those who join Jesus for the battle to come...
"And they went up into heaven in the cloud, and their enemies saw them." (Verse 11)
Verse 11 is referring to the time Paul talked about where the anointed are all gathered with Jesus in the clouds of heaven for the marriage of the Lamb, at the time of the battle of Armageddon, when every eye will see them.
The "two witnesses" won't be identifiable until the great tribulation begins, as can be seen by verses 5-12 of that chapter.
Verse 1 of Revelation 11 is talking about when worship on earth is being "measured". This is referring to after Jesus takes the throne in heaven when he refines the Christian congregation on earth. Jesus also clears the Devil out of heaven at that time, which is why the great tribulation begins and the "two witnesses" are prophesying in sackcloth, because the Christian congregation will be "trampled" by the UN.
Summary: The "two witnesses" are not a "class" of people. Just like Zerubbabel and Joshua and Elijah and Moses and John the Baptist were specific people with specific assignments, so the "two witnesses" will be two specific people with assignments during the great tribulation that relate to announcing plagues on false worship and the kingdoms of the world that are in opposition Christ once he takes the throne in heaven. The time period is during the 3 1/2 years of the great tribulation.
