Youth culture movies: how soon is too soon?

The guardians article about youth culture discusses when it is a appropriate to produce a youth culture film after it has happened.

It makes valid points about producing it too early, because the culture movement may still be going on and it hasn't yet been summarised. For a youth culture movement to be summed up and described correctly, the movement must have stopped, otherwise you won't be specific about the youth culture, because the lines would be blurred between during and the end of the movement.

Also producing a film too late - The connection between those who were involved with the movement we be lost or remebered vaguely, due to the deterioration of memory. The truth of the movement would be slowly lost and juxtaposed with the media telling you what it was like. 

I think, ideally there should at least be a 10+ year waiting period, because that will allow for the movement to end due to the next generation to begin. The issue mentioned int  the article is about how true it is to the historical events