In my experience, the computer system is programmed to charge the lesser of the weekly rate or the daily rate times x, regardless of the values.
Even if it were something insane like the weekly rate is $150 and the daily rate is $50, whether you have it for three, four, or five days, you will still pay only $150.
Barring a computer glitch, at no time would you ever pay more than the weekly rate.
The only time a rate might get recalculated would be if you book a weekend rate that requires a certain number of weekend days and you do not meet those requirements. Depending on the weekend rate, it is possible for one weekday to be more than two weekend days.