All in is used in poker (Mr. Sweetpersimmon is a poker dealer) to bet everything you have. There is nothing in reserve, you either win it or you are out. How does this relate to chado? When people say that they want to be present in the tea room ... it has to be all in. Either you are present or you are not. You have to be all in.
A lot of the ritual of chado is help the guest (and the host too) become present. As we enter each doorway or gate, we leave something of the world outside. The traffic, school work, your mother-in-law, each and every time you step through a doorway you become less and less burdened. As you put on your white socks, you put on your being present cloak, as you rinse your hands at basin, you wash more of your cares away. As you come up the steps to the tea room you are elevating yourself from the dust of everyday life, so that by the time you enter the tea room, you can be present -- nothing matters so much as what is happening at this very moment -- you are all in.
Sometimes, especially at night after work, we do about 10 minutes of zazen before we start class. This also helps us become quiet, slow our breathing, and ready for class. Just 10 minutes where your breath is the only thing that matters.
Maybe it is possible to become present any night of the week. As you leave work, you pass through doorways, you can leave work at work. As you drive home in traffic it can become your zazen. When you finally open the door and enter your home you can be all in, fully present.