Issue with db_query related to date
Instead of using different select boxes for month, date and year, you could use date_popup type.

$form['start'] = array(
    '#title' =&gt; t('Arrive'),
    '#type' =&gt; 'date_popup',
    '#default_value' =&gt; 'YYYY-MM-DD 00:00:00',
    '#date_year_range' =&gt; '0:+3',
    '#size' =&gt; 12,
    '#required' =&gt; true,
  );


Which comes with time field, so you will have the timestamp. Thats it, now you can compare the timestamp input to the database value.