Hi @huwrowlands
I’m afraid the ordering post by subfield is not possible. What you can do is creating a dummy fields that will hold the time field for the post. That way you can query the post normally. This page should give you more idea about it: https://www.advancedcustomfields.com/resources/orde-posts-by-custom-fields/.
If you still need to order by the subfield, I’m afraid you need to use the wpdb class instead. This page should give you more idea about it: https://codex.wordpress.org/Class_Reference/wpdb.
I hope this helps 🙂
