Ideally you need to spend at least a week on each step before moving up to the next and two weeks is better. Otherwise you could regain weight due to your glycogen stores (and water) refilling as soon as you start to eat extra calories (especially if carbs are involved - which they are on the higher plans).
I always try and plan ahead with my clients and get them on at least Add a Meal if they're having a week with events and things happening, but it's not ideal to keep going up and down the plans in a short space of time.
HTH - if you want any more info, please shout.