This past October, the City of Fort Collins went to a Time-of-Day (TOD) pricing structure for all residential customers. To keep it somewhat simple, it's a "supply and demand" situation. There are "non-summer" and "summer" seasons and "off-peak" and "on-peak" hours of the day.
Today is May 1st, so TOD says we are now in "summer" mode and the "on-peak" hours of higher energy costs will be between 2-7pm weekdays only. According to the City of Fort Collins website, "off-peak prices are approximately 70% less than on-peak prices."
Here is a quick and easy to follow video they have put together to explain TOD and when to crank the stereo and AC without it costing you more money: