This very much depends on the complexity of an organizations email setup. The OnDMARC app will only recommend that you move to full DMARC reject after a full 7 days of no authorised traffic failing.
Some factors that determine how long it takes to reach full protection include:
The complexity of your email setup
How many sources you send from
How active you are on completing the actions given to you
On average, it takes our customers 8-12 weeks to achieve full DMARC reject, when they book our Compliance Program