I talked to the utility inspector here in Vegas when he came to "inspect" (really was majority just to swap meters) -- he said it's pretty common that people here will turn their system on before they get PTO.
He said the main problem with that is that the standard meter's tracking device only measures total "power movement" and does not
discern direction/flow -- so you end up getting billed for usage
on any energy that you're exporting --
the meter just doesn't know the difference. As long as you don't export, then it's not a big deal; meaning you need to keep it to net zero OR disconnect from the grid, until you have a meter that can make the directional distinction, between incoming-vs-outgoing energy.
I'm simply relaying what the inspector told me here in Vegas, though I don't think he had any reason to lie -- he was actually a super nice guy and extremely friendly, answered a bunch of my random questions about the process & it's timing (he was doing >20 meter swaps a day, every day; all the 'lag' is from the paper-pushers, it sounds like). YMMV, just relaying what I was told.