Answer:
   
   B'shaah Tova can be translated to mean "in a propitious time", which
   implies that any type of positive occurance in life has a possibility
   of happening at any point in time that may be good or bad or anything
   in-between, and that a wish that it happens at a propitious, or "good"
   time has an impact on the event itself. This is also another way of
   saying Mazal Tov, which translates to mean ""Good Luck" or "May the
   Mazalos impact you (or this event) for the good." Most people who say
   Mazal tov usually mean to say "congratulations" or "I'm happy for
   you". However, "BeShah Tovah" and "Mazal Tov" have virtually the same
   meaning.