my $timer;
$timer = Timer->new(
   callback => sub {
      ...
      if (...) {
         $timer->cancel;
      }
      ...
   },
   period => 5,
)

##</code><code>##

my $timer = Timer->new(
   callback => sub {
      my ($timer) = @_;
      ...
      if (...) {
         $timer->cancel;
      }
      ...
   },
   period => 5,
)