the synergy you will get stacking NPP and test together makes it in your favor to start them together. that is a mild anabolic with an androgen. DHN with a DHT. etc. that is why we stack steroids. so IMO starting them from day 1 TOGETHER is better.
but if you want to do it your way that is fine, if that floats your boat. essentially all things being equal by week 6 you will have greater results had you started them week 1 together.