Having seperate pricing based on hour.

Hello,
I just installed your plugin and everything is great. Except I need a way to charge different pricing based on hour of the day. For example, if someone schedules a dog walk between 10am - 6pm then the price is $17 per 30 minutes. If the time is outside of this schedule, for example, 8pm then the price needs to be $22 per 30 minutes. How can I accomplish this?