Thank you very much but there are two problems that I already solved and that maybe can help someone else:
1) The date must be in the format Y-m-d.
2) To insert the code in the page it should be wrapped with this function in order to work:
jQuery(document).ready(function($) { CODE HERE });
AGAIN THANK YOU VERY MUCH FOR THE GREAT HELP AND FANTASTIC PLUGIN DEVELOPMENT YOU DID