Hi There,
Thank you so much for getting in touch with us, and our sincere apologies for the delayed response over the weekend.
You will be able to execute a jQuery script once all the markers loaded on your map by adding your code in the following function below:
jQuery(window).on('markersplaced.wpgmza', function(){
// Your script
});
Please do let me know if this is working for you and I look forward to hearing back from you.
Kind Regards,
Abel