my $ref_time = time();
my $ref_delta = $serverRef->{ScanErrlogLastDays}*24*3600;

while (<LOG>) {
    next unless ( /^\s*([\d\/\-]+\s+[\d\.\:]+)\s+/ );
    next if ( $ref_time - str2time( $1 ) > $ref_delta );

    $ref->{start_check_datetime} = $1;

    # put all the stuff from the second while loop here
}

# all done, and you didn't miss the first record

##</code><code>##

my $seeking = 1;
my $ref_time = time();
my $ref_delta = $serverRef->{ScanErrlogLastDays}*24*3600;

while (<LOG>) {
    if ( $seeking ) {
        next unless ( /^\s*([\d\/\-]+\s+[\d\.\:]+)\s+/ );
        next if ( $ref_time - str2time( $1 ) > $ref_delta );

        $ref->{start_check_datetime} = $1;
        $seeking = 0;
    }

    # put all the stuff from the second while loop here
}