It seems like one or two desks get manned at some point around 4 hours before the flight with no guarantees, hence it can be 3.5 hours. I finished my run and got to the desk about 3h45 before departure and was among the first pax to be checking in at one desk. Straight to the QF lounge for a shower after (though I realized had I taken a towel I could have taken one just outside the airport at the end of the jogging track as well).