single chargin rate with different prices based on date

In this months energy prices are changing quite often, so I would like to change the price for my home charges based on date. Currently I am creating different charging rates based on date, but this is quite bad, the number of duplicated charging rates is only going to increase over time, and to do this I can only set the charging rate after I have received my bill. Using a single charging rate with different prices based on date (like we can do based on the day of the week and time) would be much better