Realistically at least 3-4 years, assuming they want to keep the same goals as eIDAS. I think the (software) implementation will be the least costly part, time-wise; but it takes a long time before everyone adopts a new social system. Especially in the US where there has been no precedent for digital identification. Even with full control of your own ID & and solid implementation details, there will be push-back just for suggesting that people/companies should adopt it.