It is for example here:
Your Qualified title will expire one year after the date when you pass the Google Advertising Professional Exam. For instance, if you pass the exam on Jan. 1, 2005, your Qualified title will expire on Jan. 1, 2006.
BUT
I just found this:
Your Qualified title will expire two years (24 months) from the date when you pass the Google Advertising Professional Exam. For instance, if you passed the exam on Jan. 1, 2005, your Qualified title will expire on Jan. 1, 2007.
I think AWA can clatify this.