In VoucherCart, you can set:
a) A start date and an end date between which the voucher holder can redeem his/her voucher. This is specific to every voucher you create and is called the Redeem Window. This is ideal for events for example, where you are selling tickets to an event taking place on a specific day or set of days.
b) A period after date of purchase during which the voucher holder must redeem his/her voucher. This is called the Voucher Expiry Period and is the most common format. 3,6,9 or 12 months are most common.