At most Zen Sesshin I know, folks sit many times a day, for 30, 40 or 45 minutes at a time, two or three times back to back, in many sets each day. Most intersperse work periods, lecture periods, eating periods, break periods, sleep period, chanting periods ... but all are one, continuous flowing Zazen in its wider meaning. Most still have lots and lots of sitting on the Zafu sitting (especially in Soto Zen).
Now, someone might ask too, "if each moment is all time and space, and Zazen is 'good for nothing', what is the purpose of an intensive Sesshin?" Well, I often say that, sometimes, we need to practice a bit long and hard, morning to night ... sitting and wrestling with 'me, my self and I' ... all to achieve nothing to attain, and taste the good of 'good for nothing'! Going to Retreats, Sesshin and such is a powerful facet of this Practice and not to be missed.