I think that 20 hours of CEU's is reasonable for 2 years.  It would depend on the definition of a CEU, because many institutions do not have formal educational processes in place. I don't think they should require retesting after inactive, because of the expense and timing issues.  I really think that supervised work is a better option.  I would think that institutions should have a probationary period in place so that they need to be supervised for a period of time anyway.