I was having trouble extending the cookie lifetime setting in:

MASTER SETTINGS > PRIMARY > COOKIE LIFETIME

After grepping the code, I found that the following files hard-code a 1-week maximum (version 7.7.1).

I honestly believe that the configured setting set by the admin should be preserved. I hope this can be updated in a future release.

Thanks in advance for considering this suggestion.

Here is the code:
PHP Code
if ($config['COOKIE_LIFETIME'] > 2592000) $config['COOKIE_LIFETIME'] = 2592000;

List of files:

Code
admin/loginas.php # Line 64
install/install.php # Sets default value. Don't know if it resets existing setting.
install/createtable.php # Line 2581
libs/html.inc.php # Line 1502
scripts/changebasic.inc.php # Line 642

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Tomorrow they call you "ahead of your time".