SOPP563: When is the optimal moment to decide the fingering?

This question was sent by Daniel, and he writes: “Hello Vidas and Ausra! I have a question about fingering and practising in a very slow tempo. If I do the fingering early I often have to choose another solution when I know the difficult parts better and can play them in a ”final” tempo. So the question is: When is the optimal moment to decide the fingering? Thanks for all good inspiration!”