use strict;
use warnings;

open my $fileA, ... or die;
open my $fileB, ... or die;
# same with the other files

my $lineB = '';
while( my $lineA = <$fileA> ) {
  chomp $lineA;
  next unless $lineA =~ m/^\d\.+(\d{2}):(\d{2}):(\d{2})\.+(\d{2})(\d{2})(\d{2})\d{2}.abc/;  
  my $dateA = ... ; # construct date from $1, $2 etc
  do {
    chomp $lineB;
    next unless $lineB =~ m/^\d\.+(\d{2}):(\d{2}):(\d{2})\.+(\d{2})(\d{2})(\d{2})\d{2}.abc/;  
    my $dateB = ... ; # construct date ...
    next if $dateB < $dateA; # use some date and time library for these comparisons
    last if $dateB > $dateA; # ...
    $lineA .= $lineB;
  } while( $lineB = <$fileB> );
  # same with fileC etc...
  print "$lineA\n";
}