Understand the T&C. But what's the intention behind it?

Is it that if they removed the Sat night requirement, it will be too rewarding for customer loyalty?

Is it that there is actually a lot demand for one day rental, that they can't afford to give it away?

Is it if they get the car back early, they don't have enough room to park it?

T&C doesn't always need to make sense. I guess to some extent it's futile trying to understand it...