I'm not 100% certain quite what you're asking - if you mean when does it actively grow, like every other plant, during the growing season is the answer, which is roughly April through till October. But it retains its leaves all year and remains green.

I thought that but mine is starting to grow now, it lay dormant till now? thank you for your answer...

Too much heat and insufficient water possibly?

Sometimes new plants will sit growing roots for months after planting, with minimal top growth.

My Box balls have started to re grow just now but I am going to leave them to their own devices, if they continue I might give them a little trim before the winter. I have always been told to cut box on derby day, not sure why!! Also bear in mind this has been one very crazy year as far as seasons go !!