I now feel that the 120 year warning was warning of a time that the fabric of the universe of man would be changed, and the spiritual and physical no longer together. If you recall, the tower of babel, and the 'division' of Peleg's day fell about 120 years after that warning.
Peleg, according to a very popular and accepted method of chronology, was born 101 years after the flood. If this warning was 19 years, or so before that, we still had a lot of time for the year of the flood, and building of the ark as well. No need to go with the old idea that it was the flood that the warning referred to, and that it took 120 years to build it.
Edited by simple, : No reason given.