Untested, but the following should only change the expiration time for admins who select ‘remember me’.
function wpse108399_change_cookie_logout( $expiration, $user_id, $remember ){
if( $remember && user_can( $user_id, 'manage_options' ) ){
$expiration = 60;// yes, I know this is 1 minute
}
return $expiration;
}
add_filter( 'auth_cookie_expiration','wpse108399_change_cookie_logout', 10, 3 );