I didn't quite get what you were asking.
If you are referring to the actual custard component... I bring to a boil and then shut it down to a simmer.
It is done when the mixture coats the back of a spoon.
Times will be different for just about everyone depending on elevation, ambient humidity, type pan used and so forth and so on.
I would make the caramel and then let it cool sufficiently to be added to the anglais and the whipped cream; in my experience I don't let it cook after adding the warmed cream. I like a very dark caramel otherwise to my taste it gets diluted after you add the anglais and whipped cream...