my @matched;
foreach $file ( @filelist ) {   # or a while loop...
    my ( $fdate, $ftime ) = ( $file =~ /(\d{6})(\d{6})$/ );
    if ( ( $fdate >= $start_date ) && ( $fdate <= $end_date ) 
         && ( $ftime >= $start_time ) && ( $ftime <= $end_time) ) {
      push @matched, $file;
    }
}