I have done this for a few clients. Though they have all come up with different issues, the solutions seems to be the same.
“When I take too long to edit the product, I get logged out.”
“If I leave the admin for a few minutes, I need to redo anything I was doing the last time. The system just says to me to login and all changes are lost.”

The Solution:
Find the following file:
if (!$SESS_LIFE = get_cfg_var(‘session.gc_maxlifetime’)) {
$SESS_LIFE = 1440;
}

Replace it with:
/*
if (!$SESS_LIFE = get_cfg_var(‘session.gc_maxlifetime’)) {
$SESS_LIFE = 1440;
}
*/
$SESS_LIFE = 86400;

The code may vary a bit depending on the version you might be using. But that should keep the admin session alive for 86400 ( 24 hrs x 60 minutes x 60 seconds = 86400 seconds ) seconds i.e, a Day.

The same solution can be applied to Zen cart and CRE Loaded ( or any other derivative/clone of oscommerce ). Feel free to contact us in case you need any help.

Cheers,
Shiva