You could:

$SIG{ALRM} = sub{die "too long"};

my $xSecs = 1;
my $content = "";

eval {
    alarm $xSecs;
    
    my $p = HTML::TreeBuilder->new ();
    $p->parse($content);
    alarm 0;
};

print "Died after waiting $xSecs" if $@ =~ /^too long/;
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