How and where should I override the character length of the description field for an exposed filter
After discussing it with Kevin in the comments above, I settled on a custom module to solve our problem. It's very simple and small module that includes the following:

function views_description_strlen_form_alter(&amp;$form, &amp;$form_state, $form_id) {

if ($form_id == 'views_ui_config_item_form') {
    $form['options']['expose']['description']['#maxlength'] = 1000;
    }
}