The periodic journals are used to generate the recurring vouchers without any time limit.
You can consider introducing a new field "Expiry Date" in the Periodic journal line form so that it can restrict the voucher creation till the expiry date. This can be achieved with a condition that the voucher will be created only when the "Date" field value of the periodic journal line is less than or equal to the "Expiry Date" field value.
When the "Expiry Date" filed is blank, there is no limitation of generating voucher as usual.