[eluser]tonanbarbarian[/eluser]
you should be aware however that even if the max_execution time in php is set to 1200 seconds the webserver may be set to less than that and it may cancel the upload process
also the problem with doing this is that it sets these high values for the entire site (or the entire subdirectory the .htaccess is in). This means that any other requests to the server are allowed to take up to 1200 seconds.
Someone could maliciously attack your server and overload it by starting to send a request and then breaking and letting the server sit there for the rest of the 1200 seconds waiting for the rest of the response. It they then do that multiple times your server will overload very quickly.
Chances of this happening are remote but possible so be aware