Remove seconds in time picker
I removed the seconds from the daterange widget by setting the step attribute in hook_field_widget_WIDGET_TYPE_form_alter() to 60 (seconds)

function my_module_field_widget_time_range_form_alter(&amp;$element, FormStateInterface $form_state, $context) {
  $element['value']['#attributes']['step'] = 60;
  $element['end_value']['#attributes']['step'] = 60;
}