it's not about days but number of people pre-ordering and redeeming codes on those days, if they only take 50,000 ppl per wave (don't know the exact number sure some one could do the math) and between 2 days that many ppl redeemed codes then thats how many get in, on slower days were less are redeeming it'll span more days, that is at least how I a munderstanding the wave system.