When to have NT ultrasound

I can get my next scan anywhere from 11 weeks (July 27th) - end of week 13 (August 14)

When should I? Like am I gonna see much different on an 11 w vs 12w?

I tend to be an impatient person and a worrier. Part of my wants to get it on the very first day I can but if I wait am I going to see a huge difference?

First timer over here!!!