In my case, they've been interspersed. Even features will change, as you gain more knowledge - and some things you thought as important, will turn out not to be

In my case, they've been interspersed. Even features will change, as you gain more knowledge - and some things you thought as important, will turn out not to be. I will tell you this: it takes a lot of will power to continue working, if the project is not short term. I've worked on mine for almost 2 years and I'm still in Beta.