When to switch from late flowering to maturation?

Potassium (K) is needed all throughout flowering and more so than phosphorous (P). If you haven't increased the K by now, you may be too late, as your flowers are at the stage they stop growing noticeably and only ripen/mature after this. Giving a boost of K now will not hurt though, but don't expect to see any great extra growth happening. Hope this helps, Organoman.