Here it says in 2nd, 3rd and 4th billing cycle, My first statement will be generated on 17th august so i guess my 2nd billing cycle starts after 17th august, hence i will not spend anything this month( till 17 august).
upgrade voucher is valid on revenue and points booking on a avialability basis.
you can consider the price of the voucher as the difference between the economy and premium economy fares and premium eco and biz fares