What does 'EST' at the end of a NOTAM's valid time mean?
If the NOTAM duration is expected to return to service prior to the
End of Validity time, the time is expressed by using a date-time group
followed immediately by EST (estimate).  Any NOTAM that includes an
EST must be canceled or replaced before the NOTAM reaches its  End of
Validity time. If the NOTAM is not canceled or replaced, it will
expire at the end  of validity time regardless of EST.

Reference:
https://www.faa.gov/documentlibrary/media/order/notam.pdf#page=7