Are there any isolated parts of the system that you can work on outside of the fully-built system? Maybe there's some refactoring that needs to be done, where y

Are there any isolated parts of the system that you can work on outside of the fully-built system? Maybe there's some refactoring that needs to be done, where you can do some of the work in isolation and then stage it for the next build? Also, since nobody's mentioning it, are you in a position to research/ prototype an alternative approach that doesn't take so long to build?