What Redoctober has written in plain English I will translate into legalese:
A Consent Order is binding from the date of the order and comes into force on the date of Decree Absolue being granted.
I am however a bit surprised that you do not have a date stated from which the maintenance is to start. What is there legally to stop you starting it in 2020?
If you have a Consent Order then you both must have surely agreed something. Why not implement your agreement and consign the Consent Order to a drawer from which it may be pulled out and referred to should a disagreement arise?