Drupal - How to extend duration of the the one time login link?

For Drupal 7: In your settings.php try adding this:

$conf['user_password_reset_timeout'] = '259200';

In Drupal 8, you need to add the following line to your settings.php file:

$config['user.settings']['password_reset_timeout'] = 259200;

See the documentation for Global overrides:

Drupal 8 retains the possibility of using the global $config overrides. The configuration system integrates these override values via the Drupal\Core\Config\ConfigFactory::get() implementation. When you retrieve a value from configuration, the global $config variable gets a chance to change the returned value.