Increase precision

resources/check_resmon_metric

@@ -320,6 +320,7 @@ eval {
     my $ref;
     # Make the HTTP request
     my $res = $ua->request($t);
+    my $now_after = Time::HiRes::time();
     die "could not fetch http://$host:$port$url - " . $res->status_line ."\n"
         unless($res && $res->is_success);
     # Parse the xml
@@ -340,9 +341,9 @@ eval {
     if($age) { 
       my $last_update;
       if ($module eq 'System::Time' && $check eq 'now') {
-        $last_update = Time::HiRes::time() -  $ref->{ResmonResult}->[$idx]->{metric}->{now}->{content};
+        $last_update = $now_after -  $ref->{ResmonResult}->[$idx]->{metric}->{now}->{content};
       } else {
-        $last_update = Time::HiRes::time() - $ref->{ResmonResult}->[$idx]->{last_update}->[0];
+        $last_update = $now_after - $ref->{ResmonResult}->[$idx]->{last_update}->[0];
       }
       if ($age < abs($last_update)){
         $state = "CRITICAL";