Can't answer for N40 but in homebuilt our early arrival crew is there the weekend before opening weekend. Any time during the week before, by Wednesday we have rows set up and are ready.
Of course, if you get there that early, you'd better have a good reason, ie. be part of the volunteer effort. Otherwise, you're just in the way. You also need to be pretty self sufficient if you get there any sooner than Saturday, as there is no transportation, food etc. in place.