I don't see how these graphs are any more than loosely correlated with game time. Number of accesses by runners doesn't equal turns. Number of agendas accessed by corps doesn't equal scoring.
A better measure of number of turns is that measured directly on OCTGN. Slaghund data puts the average number of turns between 13 and 16 (that is turn cycle I assume). The turn data is skewed slightly to the right, which implies more than 50% of the games go longer than 13-16 turns.
Now, of course, you don't want to set your tournament at the time it takes less than half to finish, so I did some crunching of the latest OCTGN data dump I could find (4/2014) and it turns out that 90% of games finished by turn 20. Was 4/2014 before the arrival of Redcoats and RP/ELP/Ash/Caprice? Anyway, seems like if you want most people to be able to finish 2 games in the time allotted you probably want to allow time for 35-40 turns.
Now, how long a turn takes is all that needs to be figured.