I see no reason why not do this in proper spot market way. Calculate it every 5 minutes, what you supply you get accounted for and what you use or that is withdraw you get accounted. At certain intervals these are matched and you pay the difference.
> I see no reason why not do this in proper spot market way.
The wholesale/spot electricity market is a scary place, as some people in Texas discovered last year [1]
Time of use pricing tranches are designed to insulate consumers from that sort of variability, while also incentivizing consumers to minimize consumption during peak demand times.
Time-of-use electricity pricing has been happening in California for a long time, but only now is it becoming mandatory (there are still many households out there on legacy flat-rate plans, although they are being moved).
Many parts of the country are just now introducing time-of-use pricing. As both the grid and loads become smarter and more resilient, we'll see consumer electricity rates reflect the underlying wholesale price variability even more, but probably never completely.