You can set hourly rates for each venue under Settings > {Venue Name} > Hourly Rates tab
There is a default hourly rate, which is used for your most common rate. Then you can set rate exceptions with date, day and time below.
Example: If you run a business with prime ($200/hour) and non-prime ($100/hour) rates during the day, set your most used rate as default and then add your other rate to override during preferred periods.