I think if you streamline the process you can bring that number down considerably. I wouldn't want to hazard a guess at an exact number of what's reasonable and what's not reasonable, because I think that's an incredibly subjective thing.
The other thing that regulators can do is put in interim measures, as they did with fishing vessel stability. You put in interim measures that are not necessarily legal requirements until you can get the legal requirements in place.
In aviation, there are similar tools in airworthiness directives and such.