Sivel, From within LWP::Simple you can still use other LWP methods, just import the useragent object for this purpose.

So in your example to set a timeout of 10:

use LWP::Simple qw($ua head);
$ua->timeout(10);

my $url = 'http://www.domain.com/';
if (head($url)) {
  print "Does exist\n";
} else {
  print "Does not exist or timeout\n";;
}
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NB: LWP::Simple's head() and get() functions do not distinguish between 'not exists' and 'timeout', it returns similar for both situations.