In order to rest and stretch our legs between periods of stationary meditation, we practice walking meditation.
In the formal version of waking meditation, the head, shoulders, back, eyes, breath, and awareness are as in sitting meditation. The hands can be held as in sitting meditation. Alternatively, one can make a fist of one hand, tucking the thumb inside the fist, and positioning the fist in the center of the chest at heart height. Place the other hand palm down on top of the fist, and hold the elbows at the same height as the fist with the forearms parallel to the floor.
The walking is a slow continuous motion with short steps. We breathe synchronously with our steps, usually breathing in on one step and out on the next.
The length of individual meditation periods should vary with need and opportunity.
When meditating alone, pick a length that is comfortable, but pushes the comfort zone. Periods of around a half-hour work for many people.
When meditating by yourself or with others, it is a good idea not to go beyond forty-five minutes without a break to rest the legs, unless you are comfortable with such longer periods.