Wordpress Plugin (directories) fontendsubmit datepicker

One of my Plugins in a Directory-Website with frontendsubmit wont take the opening hours into postmeta.
I was looking to check everything, but i can not find the correct part of the code to fix it.

Theme is listeo and plugin is listeo-core. In a frontend-form the user can edit or add listings.
inside the submit-form is a field for opening hours.
if the user activate that field, a postmeta "_opening_hours_status" will inserted to databse with value "on". Thats wordking finde.
But if the user put times in the opening hours, the postmetas like "_monday_opening_hours" dont appear in the database, but have to.
(if i edit the listing in backend, i can edit times and it works fine. It's just the frontendsubmitform what causes the missing insert.)
Should be a really easy task, as i think the flatpickr (datepicker) is causing the problem, cause in backend a different datepicker is in use and works finde. maybe that datepicker dont insert the times into the text-fields and the insers are just empty (and if empty, nothing will be inserted into db.)

Code Snippet of the form for opening hours (for you to see how php is written. its well documented and easy-to-read):







<input type="text" class="listeo-flatpickr" name="__opening_hour" placeholder="" value="



<input type="text" class="listeo-flatpickr" name="__closing_hour" placeholder="" value="