Banking laws enacted after the Great Depression forbid US banks to be closed more than 4 days in a row, hence nearly all time locks meant for US use do not exceed 96 hours. Most time locks end at 72; three days. Although there are models that extend to 120 and even 144 hours 6 days which may be used for non-Federally chartered banks. When was the last time you noticed a bank closed for longer than three days?
via My Time Machines.

A bank vault time lock in rural West Tennessee.

A few months backs, we installed some new equipment at a municipal (city) library. The library building had previously been a bank, and the bank vault, vault door, and time lock were still in place. I took a few pictures and it piqued my interest in vault door time locks.

I knew that banks weren’t supposed to be closed for more than 4 days (and that’s still the law), but never imagined that time lock makers accounted for that.