Allot is individual as well.. I have played around with dosing(250 eod, 250 e3d, e4d, 500 e3d, etc) I find i feel best dosing 500 every 3rd then 4th day(mon/thur)..
Nos- i feel you bro, for me it seems right around 3wks, as soon as i crack a new one, it is a NOTICEABLE difference.. Next time i am ordering all 1500iu's. It is more pricey, but IMO worth it.