I actively follow electricity prices as I have the spot pricing contract. Just doing a bit of homework and timing most energy consuming things can save me some money. Of course the largest usage comes from charging the car and especially knowing when to charge it can have a huge effect on my electricity bill.
The prices vary quite a bit. Mostly from day to day, but also within a day. The service I use to monitor the hourly prices nicely uses different colours for various pricing tiers: when it's cheap the prices are green, average prices are blue and expensive ones red. Quite logical.
The problem is, from day to day those thresholds can vary. They are dependant on the daily price average so one day green could be anything below 0,5 cents while other day the "cheap" cutout might be 5 cents! This sure helps to make decisions within a day, but if you need to compare whether to postpone something for another day it might give a misleading impression.