If so, my advice to you would be to change your invoice register to be timeless (I don't believe invoice details are meant to change over time; maybe corrected every now and then but not reviewed every month).
Even so, the only thing you need, is to calculated a cumulative theoretical balance and a cumulative actual balance in order to figure out the adjustment or true-up amount that you need to post. When you have it, it's a matter of linking it to the current month based on your model time setting.
You need to set up a properties module for you invoices list which you can use to define the expected payment delay. If your target module is dimensioned by period month then in you properties module allocated a number for each invoice that indicates how many months you expect to wait for payment. In your target module we can use the function POST to post into future periods based on the number entered in the properties module for each invoice. In the forecast cash line item use a formula such as the following; = POST(closing balance, properties module.expected delay) The formula will offset and post the value from the closing balance line item the specified number of periods forward into future months.