This also depends on the country. Where I live (Europe) the rate now changes by the minute, or thereabouts. That was made possible after everybody had to change to wireless meters. Sometimes you'll get a warning in advance - a newspaper may write "If you live here or here, don't do your cooking at this particular hour". Some providers still have fixed rate options, some apparently don't. What I dislike the most is that they're trying to force us to run our washing during the night, something the insurance company and the fire department warn intensely against. And I don't want to be at sleep if a fire starts (which happens here and there, through the year). But that's what the pricing scheme tries to enforce.