This can be achieved using PHP to order the array of posts.
You will want to use the
get_posts function instead of
WP_Query query to obtain an array of posts.
Looping through the array, you can load the custom field data and create an order array which you can then use to sort the
This idea is covered in how to sort a repeater field: http://www.advancedcustomfields.com/resources/how-to-sorting-a-repeater-field/
The only potential issue is that you have used a repeater field to allow multiple start / end dates. Perhaps you have done this for aesthetic reasons, but it will make the sorting much harder.
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