Charitably guessing that if they don't know how long they'll need to keep airspace closed then you give yourself plenty of time and rescind early if necessary, as opposed to continually issuing extensions which could cause confusion.
Indeterminate end dates are not a new problem.
For example, see the Disneyland TFR (FDC 4/3635): https://tfr.faa.gov/tfr3/?page=detail_4_3635