YES.
if u go into estudent and go to finances, you will likely see your 1st sem units (those due now) owed in red, and the other units for 2nd sem in white.
So basically, if u missed paying the upfront partial payment to obtain the discount, then u will be abe to pay it in sem 2 for sem 2 e.g. $500 and you will be eligable for the 20% discount on sem 2 ONLY, as u missed the date to obtain this in sem 1.
Hope this helps.
by the way, the debt due in red will/should be cleared if your a full hecs student e.g. it will be offput regardless of your partial payment or not, as the 500 bucks is just to give you a discount of 20% for that sem, it basically just increases their cashflow ....well this is my opinion of why they are offering it.