My advice:

If recent period is 3 weeks and you are going for a 6 weeks trip, your start page could be empty during 3 weeks.

Solution:

1 - [extension by rub] Dynamic Recent Period (install / activate / change the number of periods)
This plugin will change the recent period to have recent pictures in any case.
It changes the recent period based on upload dates (you can consider to have the 3 last upload dates as recent even the last one is 3 years old).

2 - [extension by Piwigo Team] LocalFiles Editor (install /activate)
First tab: Config

Code between <?php and ?> like this:

<?php

// random_index_redirect: list of 'internal' links to use when no section is defined on index.php.
// An example is the best than a long explanation :
//
//  for each link is associated a php condition
//  '' condition is equivalent to 'return true;'
//  $conf['random_index_redirect'] = array(
//    PHPWG_ROOT_PATH.'index.php?/best_rated' => 'return true;',
//    PHPWG_ROOT_PATH.'index.php?/recent_pics' => 'return is_a_guest();',
//    PHPWG_ROOT_PATH.'random.php' => '',
//    PHPWG_ROOT_PATH.'index.php?/categories' => '',
//    );
$conf['random_index_redirect'] = array(PHPWG_ROOT_PATH.'index.php?/recent_pics' => '',);

?>