Leap 4 - Two fussy parts?


So in the app, Leap 4 says “The first phase (fussy period) of this leap into the perceptual world of ‘events’ is age-linked and predictable, and starts between 14 and 17 weeks…” and then “Most babies start the second phase of this leap 19 weeks after full-term birth.” So does that mean there’s a second fussy period around 19 weeks and that the abilities my daughter is learning won’t really start to really take shape until after 19 weeks? The other leap descriptions seem to be more straight forward than this one. This description makes it sound like this leap is basically two parts.