You don't even have to "sit" for these "Insta-sittings." Also, an Insta-Zazen © can be of any length, starting from but a moment until infinite time (really the same when all is timeless!). We do Insta-Zazen © at points in our day when just a bit of "Zen Mind"© will change our perspective on all things, when a touch of balance will bring life into balance...
Just standing in a creeping postal line, in the dentist's chair, when the car won't start on a cold morning, when driving and stuck in traffic, when the computer crashes, the baby is teething, waiting for the crossing light to change, the toast to toast, wherever and whenever... just do what you do in Zazen, with the Lotus Position fully optional (It tends to get in the way while driving or having a root canal, although it might work in the postal line if you keep pushing along.).