edit timestamp for level 1 users

I want all my users to be able to edit the timestamp. (Meanwhile I’m not willing to give users permission to do other things that upper level users can do.)
I thought I had the solution when I changed this…
if ($user_level > 4) {
touch_time(($action == ‘edit’));
to this…
if ($user_level > 0) {
touch_time(($action == ‘edit’));
…in edit-form-advanced.php. That enables my level 1 users to see the edit timestamp div. However, it’s still not functional for those users. If they try to post date something it still gets published immediately — and yes, the box is checked.
So there must be something elsewhere in WP that disables this feature for low level users, even if they can see and operate the edit timestamp portion of the form. Anybody know what else I might need to modify to enable all my users to edit the timestamp?
Thanks.