Robert isn’t saying you just “get 7 days”. You get nothing. You apply for, and pay for, another extension of some kind. If it is rejected, then you have to leave within 7 days.
It’s valid for 6 months from the day it’s ISSUED. If you get it 1 September you can enter as many times as you like for 60-90 days at a time until about 1 March. If you enter the last day you would have almost 9 months total.
I second Tod’s recommendation. I used the METV for 3 winters. But note the 6 months starts ticking when the visa is issued. You have to balance time to get it versus not wasting days.