those files andy are only renamed on your web server at the time of ftp upload (i.e at the daily averages/extreme upload)
other Q:
that should not be the case
and, i am willing to change the way these numbers are calculated, instead of being :
the coldest or warmest temperature from 6pm or 6am,(average, but calculated on the fly) to calculating the 12 hour average only once the 12 hour average period has ended (and the the time of occurence is not needed, just the day)