Notams are issued as required and are usually temporary with a start/end date. A Notam can be reintroduced at a minutes notice by the authority issuing it.
NOTAM. Take care, times are not Local!
Not sure what you mean by “times are not Local!”?
@Overthehill
He could mean all times in NOTAMS are in UTC.
UTC is basically GMT, so take into account BST when the times are 1 hour forward.