Here is my Eversource MA 2020 timeline.
6/13 Made $100 deposit online to get the project started. Used my own referal link.
6/19 Received notification of layout completed. Documents appeared online with paperwork for Tesla and Eversource
6/21 Noticed new 340W panels and better pricing.
6/23 Site survey completed. Also asked for change to new panels and pricing.
7/10 Received notification that they received the Town's electrical/structural permit.
7/16 Updated plan to include 340W panels instead of 330W panels and new lower pricing.
7/16 Signed updated paperwork including Eversource docs. Kicked off the path to install.
7/21 Received email from Eversource saying application received for SMART program
8/19 Received email from Eversource saying application approved for SMART program.
... Insane long wait for Eversource to approve application for installation. Was told that it could be 2-9 weeks from Eversource being paid their application fee and signed paperwork...
10/1 Email received to sign Interconnection service agreement with Eversource. Permission received to schedule installation. Was given a link on Tesla account online to do an online schedule. Picked earliest available install which was 10/20.
10/13 Received phone call from Tesla saying they had an opening, would I "mind" if they came on 10/14-10/15. I said YESSSSS
10/14 8am-5pm: Two crews arrive to do the install, one to do panel prep and wiring and the other to do the powerwall and gateway install. The inverter, powerwalls, and an electrical panel to hold the inverter and powerwall breakers were installed in the basement. They spent a few hours in the attic running the wires for the panels to an exterior conduit which runs from the wall in the attic to the basement. The electrical work was completed the first day except for wiring the panels to the inverter. No panels were placed on the first day. Eversource installs an additional meter for solar production and requires a main cutoff switch on the exterior. The socket for the new meter was also installed but bridged until Eversource comes to install it and to replace the regular meter with a net metering version. Powerwalls arrived about 25% charged and a test was done to power the house from the powerwalls.
10/15 8am-4pm: One larger crew arrived to finish solar panel install and to connect the inverter. Spent about 1 hour in the attic with the wiring to connect panels and about 1 hour in the basement to hook up inverter. The rest of the time was installing panels. I have a total of 36 panels, two strings on the main roof (15 and 12 cell strings) and another triangular shape of 8 panels in the third string. They tested the panels and they were generating. They were told by the lead guy from powerwall crew to check in with him when they were done to double check the CT configuration in the gateway. They couldn't reach him and left. What this meant is that there was indeed a problem with the CT configuration and the powerwalls wouldn't charge from the solar panels. They said they would fix this when they came back for the town inspection.
10/16 Got a call from the inspection scheduler who was aware of the minor issue and scheduled the inspection for 10/21 in the morning.
10/21 Tesla and the inspector arrive at the same time and the inspector went over the electrical. Passed with no issues. The Tesla tech stayed around to fix the CT and the system is fully operational.
As of 10/29, Tesla has not informed Eversource of the passed inspection by the town. When I exchanged email with my advisor he says that the group that files paperwork with the utilities is "backed up". So at this point the delay in getting PTO is squarely on Tesla. The documents that I previously signed for Eversource claim that they will install the new meters within 10 days of getting the paperwork including the passed inspection.
11/09 update, still waiting for PTO.
It turns out that the town had not fully signed off on closing the permit, they needed tesla to send a structural plan signed by a PE. This happened 11/6 and so the town informed Tesla they are all set. Now still waiting for Tesla to tell Eversource and for Eversource to come by to install the solar production meter and replace the ordinary meter with a net-metering version. Waiting for PTO is painful.
11/16 update. Got a text from Tesla informing me that they've finally submitted my install to Eversource. Now just waiting for Eversource to install new meters and give PTO. 2 months since install was finished.
11/19 update Eversource came by to install the net-metering and solar production meters. Power was off for 9 seconds, powerwalls kicked in to avoid issues in house. Now just need official word for PTO.
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2/24/20 PTO.
My pto took over a month after the meter install and I believe that it was nudged forward by contacting the eversource contact on
this page, under the electric distribution company contact, mentioning that I had been waiting a month since the net metering meters were installed and he replied that he would look into it and I got PTO a couple of days later. You might try contacting him, after your net-meter is installed. In my email I mentioned that I found his contact info on that page.
Eversource is contractually obligated (fwiw) to install your net meter within 10 days of being notified by tesla submission of permits closed. Meter installation delay was only a few days for me. PTO took forever (5 weeks) after that. YMMV
One might ”test” their system pre-PTO if they had a jumper in place of their production meter (like I had) if they were careful to not push power back to the grid since the typical non-net-metering meter would charge a person for power sent to the grid. Using self powered mode this might be practical. In the winter this is easier with the lower production, and if a person happened to have an EV to charge during the day. One might want to be careful to not have such a rogue system operating when a power company came by to install meters for example. After the production and net meters are installed one might be able to continue “testing” their system until PTO happens. 
