Create Dynamic Stamp for Adobe Acrobat

I have created a custom stamp in Adobe Acrobat Pro 11 from the attached pdf. I have added a form field for the date, and added javascript code to that field to enter the date automatically. Unfortunately the date remains static, and I need it to automatically update each time the stamp is used. The date format needs to be dd mmm yyyy. I need the javascript fixed, and if the underlying pdf needs to be saved somewhere specific before it can be used as a dynamic stamp, I need advice on where to save it.