{%- if include.start_markup contains '<time datetime=' and include.end_markup contains '<time datetime=' -%}
  {%- assign start_seconds = include.start | date: '%s' | plus: 0 -%}
  {%- assign end_seconds = include.end | date: '%s' | plus: 0 -%}
  {%- assign start_millis = include.start | date: '%L' | plus: 0 -%}
  {%- assign end_millis = include.end | date: '%L' | plus: 0 -%}
  {%- assign reversed = false -%}
  {%- if end_seconds < start_seconds -%}
    {%- assign reversed = true -%}
  {%- elsif end_seconds == start_seconds and end_millis < start_millis -%}
    {%- assign reversed = true -%}
  {%- endif -%}
  {%- if reversed -%}<p>Event end is earlier than its start. Check the event times.</p>{%- endif -%}
{%- endif -%}