use strict;
use warnings;
use DateTime;

my @earliestEvent;
open LOGFILE, "<", $filename || die "...";
while (my $input = <LOGFILE>)
{
  my ($dateString, $id) = split / - id = /, $input;
  my $date = DateTime->new( # use one of the constructors to 
                            # fill the date
                           );
  if (!exists($earliestEvent[$id]))
  {
    $earliestEvent[$id] = {};
    $earliestEvent[$id]->{"count"} = 1;
    $earliestEvent[$id]->{"date"}  = $date;
  }
  else
  {
    my $hourBoundary = $earliestEvent[$id]->{"date"};
    $hourBoundary->add(hour=>1);
    if ($date > $hourBoundary)
    {
      print OUTFILE "$id\t" 
        . $earliestEvent[$id]->{"date"}->datetime
        . "\t" . $earliestEvent[$id]->{"count"}
        . "\n";
      $earliestEvent[$id]->{"count"} = 1;
      $earliestEvent[$id]->{"date"}  = $date;
    }
    else
    {
      ++{$earliestEvent[$id]->{"count"}};
    }
  }
}

# then, of course, you'll need to print the remaining ones