How long is a piece of string?
Really though common sense suggests, in general, paid J travel wlll be at times that suit typical working weeks/cycles.. so departures midweek are probably less likely to have higher loads vs say a Fri or Sat departure with arrival in time for start of a new week.
of course any one particular day or date could be influenced by all sorts of factors such as a group booking, maybe a bunch of people going to a convention, or coming back from same, or something like that.
Also consider time of year in terms of this - for example there should be less paid (but more upgrade) demand for J seats around holidays and Christmas/NY.