Form Submit - Populate Title Before Validation
If you use #prefix and #suffix with display:none, it is hidden in display, but submitted and will be validated for required.
Try to use #required = FALSE and #type = 'hidden' and then set title in your submit handler.

function previous_meetings_form_alter(&amp;$form, $form_state, $form_id)
{
    // Hide the title field
    $form['title']['#required'] = FALSE;
    $form['title']['#type'] = 'hidden';
    // Callback function to execute before validation
    array_unshift($form['#submit'], '_previous_meetings_set_meeting_title');

}


And you could also use Automatic Nodetitles with which you may use token replacement.