I found two methods of solving this.
.1) Set a date backwards, relative to the current date. (I'm using 60 because I need articles from 2months back)
$model->setState('filter.date_filtering', 'relative');
$model->setState('filter.relative_date', $params->get('relative_date', 60));
$items = $model->getItems();
2) Set any preferred date range
$model->setState('filter.date_filtering', 'range');
$start_date = strtotime('-2 months');
$start_date = date("Y-m-d h:i:s", $start_date);
$end_date = strtotime('now');
$end_date = date("Y-m-d h:i:s", $end_date);
$model->setState('filter.start_date_range', $start_date);
$model->setState('filter.end_date_range', $end_date);
$items = $model->getItems();