I'm not sure about a surplus. 4-9pm are still peak hours and a quick skim of this CAISO page[1] indicates we're importing electricity during peak hours.

I think the solar generation from say 10am-4pm is where you'd find a surplus, if there is one.

At least at my home, there's only ~20% difference between peak and off-peak rates, but, if you have A/C, it still makes sense to pre-cool on hot days, back it off at 4pm and then turn it back up at 9pm if you still need the cooler temps to sleep.

1. https://www.caiso.com/content/summer-loads-resources-assessm...