ESRI's Geoportal metadata record editing has some validity checking, but error checking does not occur until after a metadata record form is submitted.  This can be a wasteful process because it involves having the client (the web browser) send a full request to the application server.  If the submitted form has data validity errors then the whole form is transmitted back to the client for editing.  One way to save the use of server resources (e.g., bandwidth) is by using jQuery to monitor information typed in html input boxes and check value validity before submitting the form.  Since, ESRI's Geoportal comes with jQuery already enabled it is relatively to add validity checks.  The first thing to do is create a custom javascript file (e.g. [geoportal_install_dir]/web/geoportal/catalog/js/custom.js).  The contents of my script are:

$(document).ready(function()

{
  $('#mdEditor\\:identification_date').mask('9999-99-99T99:99:99');
  $('#mdEditor\\:general_datestamp').mask('9999-99-99');