blog/.themes/classic/source/_includes/post/date.html

{% capture date %}{{ page.date }}{{ post.date }}{% endcapture %}
{% capture date_formatted %}{{ page.date_formatted }}{{ post.date_formatted }}{% endcapture %}
{% capture has_date %}{{ date | size }}{% endcapture %}

{% if has_date != '0' %}
  {% capture time %}<time datetime="{{ date | datetime | date_to_xmlschema }}" pubdate>{{ date_formatted }}</time>{% endcapture %}
{% endif %}