Not that much time. They have really good tutorials. The additional network plugins take a few minutes, they only really require you to add things to an android manifest, iOS is automatic. Integrating the mediator plugin is exactly the same amount of work as setting up a single ad network like Unity Ads in Unity. The portals take about 30 minutes to setup and sure a little longer if something goes wrong, but we're only talking a day of work at the most and the result is far better revenue from ads at no cost to your user experience.