Error "This value should be of the correct primitive type." for start time of "00:30"

When saving a form with the Office Hours fields that contains a value of "0300" (which represents 12:30 AM), the error "This value should be of the correct primitive type." appears for the start time of "00:30".

The module currently defines the starthours and endhours fields as integers, as follows:

  public static function propertyDefinitions(FieldStorageDefinitionInterface $field_definition) {
    $properties['day'] = DataDefinition::create('integer')
      ->setLabel(t('Day'))
      ->setDescription("Stores the day of the week's numeric representation (0-6)");
    $properties['starthours'] = DataDefinition::create('integer')
      ->setLabel(t('Start hours'))
      ->setDescription("Stores the start hours value");
    $properties['endhours'] = DataDefinition::create('integer')
      ->setLabel(t('End hours'))
      ->setDescription("Stores the end hours value");

    return $properties;
  }

The custom Office Hours validation first runs, followed by the Drupal core validations. Within Drupal's core validations, the PrimitiveTypeConstraintValidator validation fails because a time of "0300", which represents 12:30 AM, is not an integer, but rather a string.
To fix, the data definition for the time fields need to be defined as strings so they are validated as such by Drupal core. The required change is as follows:

    $properties['starthours'] = DataDefinition::create('string')
...
    $properties['endhours'] = DataDefinition::create('string')
...

This change does not change how the office hour start and end times are calculated and stored in the database.