initialize: function() {
  ...

  var blackout = '#vanilla_configuration_autopay_blackout'
  this.blackoutStartLabel = blackout+'_start_input > label'
  this.blackoutStart = blackout+'_start'
  this.blackoutEndLabel = blackout+'_end_input > label'
  this.blackoutEnd = blackout+'_end'

  ...
},

checkBlackoutDates: function () {
  var hasDates = $('#vanilla_configuration_has_autopay_blackout_dates:checkbox:checked').length > 0
  if (hasDates) {
    $(this.blackoutStartLabel).removeClass('muted');
    $(this.blackoutStart).prop('disabled', false);
  } else {
    $(`${this.blackoutStartLabel}, ${this.blackoutEndLabel}`).addClass('muted');
    $(`${this.blackoutStart}, ${this.blackoutEnd}`).prop('disabled', true);
    $(`${this.blackoutStart}, ${this.blackoutEnd}`).val('');
  }
},

setBlackoutEndDateChoices: function () {
  var startDate = parseInt($(this.blackoutStart).val());

  if (startDate > 0) {
    $(this.blackoutEndLabel).removeClass('muted');
    var blackoutEndSelect = $(this.blackoutEnd);

    blackoutEndSelect.prop('disabled', false);
    blackoutEndSelect.empty();
    blackoutEndSelect.append($("<option />"));

    for(i = startDate + 1; i <= 27; i++ ) {
      blackoutEndSelect.append($("<option />").val(i).text(i));
    }

    var onLoadBlackoutEnd = blackoutEndSelect.data('id');
    if (onLoadBlackoutEnd > 0) {
      $('#vanilla_configuration_autopay_blackout_end').val(onLoadBlackoutEnd);
    }
  }
}