[iojam]

Hexemer,

if you have a maximum execution time set for php scripts, you can execute the script from the SSH (shell) command line:
/usr/local/bin/php /path/to/vbroot/vbseo_sitemap/vbseo_sitemap.php
(command line php config usually doesn't have this restriction).

The SSH access is required for this though.

If you don't have SSH, you can exclude showpost urls from the generated sitemap (in Admincp->vBSEO Sitemap Options) - that will significantly reduce the time required for sitemap generation.