Hit that lighting bolt image on the center dash screen and play with the charging schedule. YES, you can schedule timing of the charge and rate of amps via your Rivian center screen. You might also have a call and chat with your local power supplier because some have special programs for owners of EV with extra low rates in the middle of the night so you can schedule to charge at absolute lowest rate while you sleep and grid demand is super low. Use the mobile charger that came in the 'Frunk' of your Rivan, for many folks that is more than enough to charge back to 70 percent 'full' overnight on 50amp service. You might need adapter plug for whatever variation of 50amp receptacle you have but that's easy to find on Amazon, I have several because my 50 amp plugs at work are not NEMA 14-50 (mostly 6-50 at my shop).
I am in San Diego but I charge our Rivian in the middle of the day because we have big surplus solar power right in the middle of the day. At home as much as 6k surplus in the middle of the day, at my shop it can be 15k+ surplus in the middle of the day. Since the power company is paying/crediting us nearly squat for that surplus it makes sense for us to top up the battery in middle of the day. Thus, your best strategy may be different than mine and depend on the structure of your current rate plan (or optional rate plans you have yet to ask about) with your local utility. And perhaps time to consider solar? I have not paid any residential power bill whatsoever in more than 15 years here in California, and getting close to zero power bill at my commercial building as we near 100 panels installed (despite hundreds of light fixtures, and lots of big 240v 50 amp power eating equipment).