If the wait is after pressing the Search button and before the page is reloaded, one of the ways may be adding a click handler to the search button, e.g.
$(".ew-search-panel #btn-submit, .modal-footer .ew-submit").on("click", function() { // Select the submit button, this example assumes extended and modal advanced search
Swal.fire({
title: 'Searching',
html: 'Please wait...',
showConfirmButton: false
});
});