Disable select option
Disabling single options from select lists is currently not that easy in Drupal. There are some open issues regarding the topic and a couple of suggested patches, but so far neither made it into core: 


Allow FAPI select, radios, and checkboxes to specify some options as disabled
Introduce proper Form API #types for 'option' and 'optgroup', and make #options consistent
Using form_alter to disable ONE option of a select field




That said, there is a tutorial on Exove which works around the issue, by implementing the THEME_select() hook to enable theming of individual select options using a #options_attributes key: Drupal 7 Form API select element option attributes

Using the code for your theme's template.php from the tutorial, you can disable options in your form using hook_form_FORM_ID_alter().

function hook_form_FORM_ID_alter() {
  $today = date("Y-m-d H:i:s");
  $date = "2016-11-01 00:00:00";

  if ($date &gt; $today) {
    //replace 0 with the actual index for Early Bird
    $form['your_select_field']['#option_attributes'][0] = array('disabled' =&gt; 'true');

    //set the other fields based on dates here
  }
}


There is also a module which seems to offer the same functionality as the theme code from the tutorial, but I have not yet tested it: Form Options Attributes. It seems to work in a similar fashion however and might be even a little easier to set up (since you don't need to write that theme function).