Use Time::Seconds

use Time::Seconds;
my @LIST = map {
        [ $_->[0], $_->[1], $_->[2], $_->[3], $_->[4], $_->[5],$_->[6]
+ ]
    } sort {
        $a->[0] cmp $b->[0] || $b->[4] <=> $a->[4] || $a->[1] cmp $b->
+[1] || $a->[2] cmp $b->[2] || $a->[3] cmp $b->[3]
    } map {
        my $group = $_;
        map {
            my $host = $_;
            map {
                my $service = $_;    
                map {
                    my $state = $_;
                        my $count = keys %{$ERROR1{$group}->{$host}->{
+$service}->{$state}};
                        my $ts1 = (sort (keys %{$ERROR1{$group}->{$hos
+t}->{$service}->{$state}}))[0];
                        my $ts2 = (sort(keys %{$ERROR1{$group}->{$host
+}->{$service}->{$state}}))[-1];
                        [ $group, $host, $service, $state, $count, Tim
+e::Seconds->new($ts2-$ts1)->pretty() ]
                } keys %{$ERROR1{$group}->{$host}->{$_}}
            } keys %{$ERROR1{$group}->{$_}}
        } keys %{$ERROR1{$_}}
    } keys %ERROR1;


for $_ (@LIST){
  print join("\t", @{$_}) ."\n";
}
[download]

Oracle  server1 FILESYSTEM ALERT        WARNING 85% FULL        8     
+  23 hours, 30 minutes, 4 seconds
Oracle  server2 FILESYSTEM ALERT        WARNING 85% FULL        5     
+  21 hours, 59 minutes, 59 seconds
Oracle  server1 BACKUP ALERT    DAILY   1       0 seconds
[download]

And what the others are trying to say is that:

my ($ts1,$ts2) = (sort (keys %{$ERROR1{$group}->{$host}->{$service}->{
+$state}}))[0,-1];
[download]