If you follow Lean (where "Minimum Viable Product" originates from), there's no hard split between design/implementation phases, since the whole concept of MVP

If you follow Lean (where "Minimum Viable Product" originates from), there's no hard split between design/implementation phases, since the whole concept of MVP is avoiding waste in building something nobody wants. The keyword is "avoiding waste", not "build something in 1 month". You can still waste 1mo work pretending to be fast and shipping crap, that's not the point. The time a Minimum Viable Product will take is still completely determined by the requirements (definition of "viable", budget, experience, regulations, etc).