Thanks for answering !
Maybe I didn't express myself in a clear & unique way !
But there are other free programs that are more flexible. Such as:
Timeout | Romaco Canada
Many thanks !
From a functional point, seems totally what I'm looking, hope is not full of adware and won't slow my PC down.
P.S. Do you know in parental control how de-active other browsers than Chrome (esp. IE9); as my quick test about porn shows, that Chrome locks the search in "safe search mode" and is effective, while IE9 sometimes let porn thumbnail preview, which Chrome does NOT.