Contributions

This contrib got me where I wanted to go, but was not done really well...
(needs other contrib? Database changes? Add commented-out code?)

Just add the following line to admin/includes/configure.php (or admin/includes/local/configure.php):
define('ADMIN_SESSION_LIFETIME', 5400); // - Zappo - Session Lifetime in seconds for Admin side.

Then in admin/includes/functions/sessions.php REPLACE (around line 20):
$SESS_LIFE = 1440;
WITH:
// BOF - Zappo - ONE LINE - Added Session Lifetime setting (admin/includes/local/configure.php)
$SESS_LIFE = ADMIN_SESSION_LIFETIME;


That's all folks!
Just change the setting in the configure.php to the amount of seconds you'd like the session to last.
File contains same instructions as above...

Admin Session Lifetime (v. 1.1)

Fix for session timeout in the Admin Area for osCommerce.

Session Lifetime is a SQL addin witch will allow the store
owner under the admin side only to control the length of
your session without loss of work due to interruptions
during data entry. This requires MYSQL access.
Complete instructions on how to install included screenshot image included.