In Matt 24:15-20, Jesus explained that when the AoD spoken of by Daniel the prophet is set up in the holy place, those in Judea must flee to the mountains, those in the rooftops must not go inside the house to get anything, those in the fields should not return to their houses to get their clothes. Instead, they must flee hastily. Why?
I believe there will only be ONE, and ONLY 1, great tribulation based on what our Lord Himself said. This unique great tribulation will occur when the AoD is set up. Since the great tribulation is unique, the AoD whose setting up will trigger its occurrence must necessarily be unique.
In Daniel 12:1, 2, the great tribulation or time of distress will be at the time when God's people written in the book (of life?) are delivered and when the dead will be resurrected. These events are directly related with the 2nd coming.