Start of program
  TDS             :
  :               :
  V               V
  |<----- A ----->|
  |---------------:
                  :
      TDS         :
      :           :
      V           :
      |-----------:
      |<--- B --->|

   length(A) < length(B) means A is stale
   date(A)   > date(B)   means A is stale  (notice start of program is irrelevant!)

i.e., stat() returns a TDS (time date stamp)
      -M returns a length since the start of the program