Add reading time to Jekyll without a plugin
You do not need a plugin to show an estimated reading time in Jekyll. Liquid can count the words in a post and divide that number by an assumed reading speed.
This example uses 180 words per minute:
<p>
{% assign words = content | number_of_words %}
{% if words < 360 %}
1 min
{% else %}
{{ words | divided_by: 180 }} mins
{% endif %}
read
</p>
Posts below 360 words show 1 min read. Longer posts use integer division, so the result is deliberately a rough estimate rather than a stopwatch pretending to be precise.
Use page.content if the snippet is in a layout and content is not giving you the expected value. You can also change 180 to match the reading speed you prefer.