question on the probability

Hi Author,

Can i know if the probability formula you have is based daily basis? e.g. if we have set the probability for all 5 prizes to be 100%. Each different day we have different visitors coming in and we are not able to predict the volume of them coming. How would your probability works to handle this case?

e.g. based on the scenario above.
campaign duration: 1 month
Below is the probability winning % and quantity of voucher:
100usd – 20% (quantity 20)
50usd – 30% (quantity 50)
10usd – 50% (quantity 100)

How do i configure the above in your system? How do i set the probability for 100USD voucher is 20% across the 1 month period campaign?