Secrets revealed by God to Christ and written by Apostle John in the Book of Revelation, so the Early Church would not be caught off guard by dangerous Events that were about to happen.

Rev 1:1 The Revelation of Jesus Christ, which God gave unto him, to shew unto his servants things which must shortly come to pass...

Tishri is the 7th Month of the Jewish Calendar when these Feasts are celebrated:

Feast of Trumpets 1st Tishri
Day of Atonement 10th Tishri
Feast of Tabernacles 15th Tishri

In Revelation 8, John saw an Angel with a Golden Censer: it was the Day of Atonement (the golden Censer is kept in the Holy of Holies which is only open once a year, during the day of Atonement). Then John saw this Angel fill the Censer with Fire from the Altar and cast it upon "the Earth". This was on the Day of Tabernacles when Offerings were made by Fire, Leviticus 23:36. (not on the first day see scriptures)

In Revelation 8, John also saw 7 Trumpets were given to 7 Angels, this was on the day of the Feast of Trumpets (Visions for the 2 other Feasts of the Month of Tishri are already explained in the above Paragraph).

Rev 8:
1 And when he had opened the seventh seal, there was silence in heaven about the space of half an hour.
2 And I saw the seven angels which stood before God; and to them were given seven trumpets.

The Early Church knew Psalm 90:4 and 2 Peter 3:8, 1,000 Years for the Lord is like a Day. It was not hard to calculate that One Hour for God is 41.67 Years and figure out that half an Hour in Heaven is about 21 Years. The Church knew about the 7 Trumpets of Jericho and how the Children of Israel remained silent 7 days. They understood that the Trumpets of Revelation would sound more or less over a Period of time equal to 21 Years.

I recommend to read this Study:

Secret Chronology of the Sixth Trumpet:
https://www.brighteon.com/43c084e3-8675-42e8-96f0-82787d8ff1f0

In the above Study, it was established from Scriptures (this is also confirmed by historical data), that the 6th Trumpet sounded after the first day of the Feast of Tabernacles (16th Tishri), September 21th, 66 AD.

Link to a Jewish Calendar Calculator:

https://www.torahcalc.com/dateconverter/

When the verses of Revelation 1: 13 to 15 are compared to Daniel 5: 5 to 6, and Revelation 10: 5 to 7 to Daniel 12: 6 and 7, it is obvious that Apostle John and Prophet Daniel saw the same "Angel". In Revelation 10:6 and 7, the "Angel" swore that in the Days the 7th Trumpet would begin to sound there should be time no longer. On the other hand in Daniel, that same "Angel" swore it shall be for a time, times, and an half. The Early Church was familiar with the 3 1/2 Years (1260 Days) Prophecy, so they understood this would be the time span between the 6th and 7th Trumpet. From the 1st to the 7th Trumpet there are 6 equal intervals of 3 1/2 years (6 x 3.5 = 21 lunar Years), which confirms the Silence in Heaven of about half an hour.

September 20th, 66 AD was the Feast of Tabernacles, (no offerings by Fire were made the 1st Day (see the relevant verses), the 6th Trumpet sounded on September 21th, 66 AD. During the Feast of Tabernacles, Cestius came with the Roman Army, to Jerusalem and later on retreated. Three and a half Lunar Years later (1260 days), Titus with 4 Roman Legions and Auxiliary forces marched toward Jerusalem. Based on Revelations given to Apostle John and Prophet Daniel, the 7th Trumpet sounded on March 4th, 70 AD.

When the Romans arrived and started to build their Camps, they were attacked by the Jewish Rebels, this delayed the siege of the City.

To cause food shortages, Titus allowed Pilgrims to enter Jerusalem to celebrate Passover (April 11th, 70 AD) and then he completely besieged the City.

In Revelation 10, John wrote that he saw a mighty Angel come down from Heaven and cried with a loud voice:

Revelation 10:
3 ... and when he had cried, seven thunders uttered their voices.
4 And when the seven thunders had uttered their voices, I was about to write: and I heard a voice from heaven saying unto me, Seal up those things which the seven thunders uttered, and write them not.

As for Jericho, the 7th Trumpet of Revelation sounded 7 Times, Apostle John was told to seal this information. The 7th Angel sounded the Trumpet for the first time on March 4th and based on historical Data, it can be determined that the 7th Angel sounded the Trumpet every 30 Days. The 6th time that the 7th Angel sounded the Trumpet was 150 Days after March 4th: on August 1st, 70 AD exactly one Day before the Destruction of the Temple on August 2nd, 70 AD (9th Av). The last time the 7th Angel sounded the Trumpet was 30 days later, on August 31st, 70 AD, the day Jerusalem fell.

The date when Cestius with the Roman Army came to Jerusalem is in the Book Wars of the Jews, written by an Eyewitness of the war, the Jewish Historian Flavius Josephus (free online). In this book can also be found the dates of the Temple Destruction and when Jerusalem fell.