Leaving the vehicle parked at the charger for an extended period would be a helpful option, but not strictly necessary in order for EV owners to benefit from rate arbitrage. The supply and load patterns and schedules are fairly predictable at least 24 hours in advance. A smartphone app could display a schedule of rates, to allow an owner to choose when and where to charge up. It could also display rates for energy buyback, and take account of the owner's EV model and the state of its batteries to determine when selling power back to the system could return a (small) profit.

I don't expect that rate arbitrage by individual owners visiting fast charge stations will ever become a big deal. It would be more of a game that some EV owners might engage in just for the fun of being able to claim a tangible financial return on their EV or home solar power investment. Bi-directional transfer at a charging station equipped with a BESS would be very easy to support, and would promote sales of EVs and solar panels.

There's actually one class of situation where I can see a fast bi-directional transfer capability being important. If a region is hit by a fire or disaster of some sort that will require an emergency power supply, a public service alert could go out requesting EV owners to drive to a station near the area and deliver whatever energy their vehicles can spare. It strengthens a community when its citizens have opportunities to contribute and feel good about.