Dear Thomas DLouhy
Timed quizes are available in moodle 1.4 development.
This has the advantage over Chris U's hack in that you do not have to keep hacking your site each time you upgrade. Please see here
http://moodle.org/mod/forum/discuss.php?d=4813
The protection for quizes is pretty easy and requires few modifications, all of which are in the themes folder so it SHOULD be moodle upgrade compatible.
http://moodle.org/mod/forum/discuss.php?d=3982
Tim