It looks like this process takes a long time, I am not sure that the State wants to create and use the cryptocurrency during the official currency is still used. If the State uses the cryptocurrency then automatically they will be replaced official currency.
the process of creating cryptocurrency itself don't take that long time if they are going to use source code of some coin which were published in many some website. and if the state uses cryptocurrency they will more likely not to replace the official currency but making a digital version of it and maybe considering it as secondary option for their currency