Customers are always surprised that the install is the fastest part. Three days on a typical house. The other eight to eleven weeks are paperwork.
The building permit is usually two to four weeks depending on the county, and there is nothing anyone can do to speed it up. Utility interconnection is the bigger variable: a straightforward residential application is quick, but anything with a battery or an export limit gets a longer engineering review.
We file everything on day one rather than waiting for the previous step to clear, which typically saves two weeks. What we will not do is promise a switch-on date we do not control. Ask any installer who commits to one exactly which counties they have said that in.