Hi,
Don't know if it's the same in other countries, but in France some phone providers have 2 rates : one during the work time and one for the evening/night. Sometimes also, you can have free calls during evening/night. When you have several providers, sometimes it's not the same that is the cheapest during work time and during evening/night.
Is there a way to have 2 different routes with the same dialplan, one available during work time and another during evening/night ?