Time Period Scale

Can anyone kindly explain me how does the Scale Basis indicator "Time Period Scale" works ?

I am trying to setup the system to determine a discount price condition based on the no. of days in advance the sales order is received, as compared to the request date.

for example, if order is received 90 days in advance, a discount of 5% will be given. If it is 60 days, 3% will be given and less than 30 days, no discount.

Anyone can advice a solution ? Thanks alot