Moving on...
I believe Estep is wrong here on the same basis that almost everybody's system fails. The "tribulation" is
only for 42 months or 3 1/2 years. Calling Daniel's 70th week (7 years) the "Tribulation Period" and noting the "last half" as "The Great Tribulation" is private interpretation at best. The scriptural evidence for a future 7 year period is based solely upon the intricate wording of Daniel 9.
However, the book of Revelation repeatedly yields one number (in various forms) for the "time of Jacob's trouble" - 3 1/2 years. This mysterious "first half of the week" (typically taught as a time of peace between the Jew and the Antichrist) is nowhere to be expounded upon within the scriptures,
or is it?