How to have 'Show end date' unchecked by default ?

Hello,

Instead of being checked by default, I'm looking for a way to have the Show end date checkbox be unchecked by default.

I think it is better to present less fields to the user. The end date won't always be used, so it would be better to only display it to the user that need it and who will then just check the box to see the end date input fields.

i tried this jQuery hack, the checkbox is unticked but the end date field is still there, so i'm assuming this is deeper in the date module.

$('#element-id').is(':checked');
$('#element-id').removeAttr('checked');

Screenshot

Any ideas are welcome