Your effort can be considered done when a customer whose problem you were aiming to solve provides a testimony that they have solved their problem with the solution you have provided.
If you are onboarding a mass of customers, you have to have at the same time:
- Testimonies from the customers that would be considered an excellent proxy to the general population of the customers that you are onboarding
- KPIs measurements (that were set upfront) that show proof that customers have been solving their problems with the solution you provided
If you do not have KPIs set, first do that.
Keep in mind that this definition of done is problem specific. You can have the same customer you are onboarding again and again. In fact, the more successful your solutions are, the more infinite-re-onboarding is likely.
Quite often, I use "onboarded customer" instead of "done" to emphasize that I am using the definition from this article. "Onboarded customer" usually has more apparent intent than using the word "done," which is highly overloaded.