I am allowed to do this without a permit where I live, as it is my house. (An electrician might have to have a permit) I might have spent 4 hours, but I doubt it.
I agree with you that it is one of the easier installations, but there are a few elements that come into play - with this level of continuous current, torque of connections (and occasional re-torque) is absolutely key for safety, at both the circuit breaker and receptacle. In addition, for conduits you need to make sure you have the proper insulating bushings, which is different from typical 12/2 NM installation with a clamp. If you pay attention to those, it's pretty easy and you can save money by doing it yourself.
With regard to permits: typically, a homeowner is allowed to do the work without being a licensed electrician, but still requires a permit and inspection (sec 7044(a), CA Business and Professions Code).
Napa County appears to require a permit, even if you're a homeowner. It adopts the 2013 California Electrical Code in Napa County Code 15.28.010:
15.28.010 - Documents adopted by reference.
For the purpose of establishing proper regulations for building construction and for the installation of electrical systems, the provisions of the 2013 Edition of the California Electrical Code, hereinafter referred to as "electrical code," including Annexes A through H, which is based upon the 2011 Edition of the National Electrical Code as adopted with modifications by the State of California as Title 24, Part 3 of the California Code of Regulations, is adopted and made a part of this code by reference.
...and the California Electric Code requirements for permits:
89.108.4 PERMITS, FEES, APPLICATIONS AND INSPECTIONS
89.108.4.1 Permits. (a) Except as exempted in paragraph (b) of this subsection, a written construction permit shall be obtained from the enforcing agency prior to the erection, construction, reconstruction, installation, movement, or alteration of any electrical system.
(b) Consistent with the requirements of Section 17960 of the Health and Safety Code, the local enforcing agency
shall enforce the requirements of this code, but shall exempt the following activities from the requirement for
a permit or inspection.
1. Listed cord and plug connected temporary decorative lighting.
2. Reinstallation of attachment plug receptacles, but not the outlets therefore.
3. Repair or replacement of branch circuit overcurrent devices of the required capacity in the same location.
4. Installation or maintenance of communications wiring, devices, appliances, apparatus or equipment.
Exemptions from permit and inspection requirements shall not be deemed to grant authorization for any work
to be done in any manner in violation of any other provision of law or this code.
Section 15.28 of the Napa County Code addresses some changes for vineyards and keeping work space clear for PV system equipment, but does not modify any of the requirements for permits in 89.108. The chief electrical inspector is defined as the county building officer.
They list fees for electrical permits @ $79.33 for rough + final. They note "same day" permits for minor electrical & plumbing, and specifically list types 1 & 2 EVSE installation. Their permit application requires you to make a declaration that either a) you're the property owner and it is not a commercial building/offered for sale, or b) you're a licensed electrician, so the application doesn't seem to exempt property owners. I will say, though, that their site is pretty confusing and tends to cover mainly erection of new structures - but the code reads to require permits for installation of new receptacles and branch circuits and I see nothing that tends to exempt homeowners from permit/inspection requirements.
That said, the county building officer gets to make the call. A phone call to the county building office will determine it - I would call them before doing any work in the future to confirm whether or not a permit is required. All the places I've done work required permits and inspections for homeowners, but did not require a homeowner to be a licensed contractor unless the building was a commercial building (or, sometimes, was leased to tenants).