You could also look to the 120 year proclamation in Genesis 6 right before the flood. One could conclude that God sets dates for end times because he determined a countdown to the flood. The problem here is the interpretation of a countdown only comes from the legend of the Jews. See Luis Ginzberg's Legends of the Jews. The witnesses stick to the countdown belief. This makes date setting justified with the Org.
The two opposing interpretations of the 120 years in Genesis is a countdown to the flood or the reduction of the human lifespan. The births and deaths of the antediluvian people in Genesis compared to the generation of the post flood world did prove that the lifespans were decreased. The 120 years maximum could be a general rule and would have a margin of error but it definitely matches better than a countdown to the flood. Also of note is that the early part of Genesis records so many lifespans of people then later on the bible mentions only a few important ones. Abraham died at 175, Moses died at 120, Joshua died at 110, David died at 70. The lifespan settles down to around 70 to 80. Some today have been able to reach 122 but it is so rare.