while ( <DATA> ) {
    chomp;
    my ( $number, $time ) = m{
      (\d\.\d{3})      # a number with 3 decimal places
      .*? , \s*        # some characters, a comma and some spaces
      (\d\d:\d\d:\d\d) # HH:MM:SS
    }x;

    print "$number,$time\n"
      if defined $number && defined $time;
}
__DATA__
1.4567 ,11:00:00
1.4571 ,11:00:01
            ,
1.4567 ,11:58:00rftft
1.4566 ,
1.5555 ,11:43:00