The honest truth is that even ONE second of pure stillness is a massive achievement and a perfect tool because once you get a "taste" of what stillness is like, you will realize that you have access to this state of mind anywhere and anytime.
For example, let's say you're about to go into a big meeting and you're overrun by anxiety? You could consciously remind yourself that you have absolute power over your mind and may decide to go to a quite spot (cubicles are surprisingly good -lol ), sit there and centre yourself in stillness.
I would recommend sitting for between 5-15 minutes initially. You may find it useful to make us of relaxing, soothing music () and read up further on the topic (Why Meditate - Mattieu Ricard)
RE: How To Meditate - A Prelude to your own Superpower.