D7 visa application. How long does the initial hotel / Air B&B stay need to be

We are in the middle of gathering the information for our D7 visa application. Unsure at this point how long the initial stay needs to be when we first arrive. We have friends who we can stay with but it may be more convenient to get an Air B&B. All help appreciated

there is a lot more useful information on the D7 process in the files in the FB AFIP group than there is here.