Read perldoc -f alarm if you haven't already.

A quick way to do what you want:

    
    $MyRequest = HTTP::Request->new('GET',"$URL");
    alarm 30;
    $MyResponse = $UserAgent->request($MyRequest);
    my $timeleft = alarm 0;
[download]

Caveats: Too many to list in this space, signal handling has the ability to wildly complicate your life, etc. If your program is very simple I think the above may do what you need. If not, Super Search for examples and ask more questions. :)