I am currently doing this with a hidden field set up as an integer and displaying a text field which is converted to an integer by code and used to set the value of the hidden field in the Submit function:

$date101 = $form_state['values']['deadline2']['year']."-".$form_state['values']['deadline2']['month']."-".$form_state['values']['deadline2']['day']."00:00";
$form_state['values']['deadline1'] = strtotime($date101);

Whilst this works, I am sure there must be a better approach ! I hope someone suggest the right way to do this. Thanks.