Following the bike fit there is a 4 week period of adaptation which is necessary to allow the body to become accustomed to new motor patterns. During this time the position may feel awkward or not as powerful. This is all dependent on how much your position has changed and how long you have been riding. After this, there are as many return visits as necessary within a three month period to dial the position in further if need be.
After a bike fit I advise that you ride at a steady pace for 2-3 weeks. This means Zone 3 and below or 75 % of maximum heart rate. Therefore it is best to book a bike fit well in advance of an important event/race.
This service is only provided that the optimum position can be achieved (bike and shoes actually fit) and all necessary changes needed are made.
This can also apply to different saddles and equipment. For example when swapping to an ISM or Selle SMP saddle, you will be sat on different parts and loading new areas (and hopefully unloading sensitive areas). I generally recommend trying a non standard saddle (ISM, SMP, SQ Lab) for 10 days assuming it is not causing numbness or pain.