On average we play from 8 to 10:30 eastern. Sometimes 3-4 people will make it past that barrier and we'll play a small mission or Invasion 'til 11-11:30 or so. If 8 is too early, it's fine to come in later. You may have to wait around until the mission ends, but just alt-tab out and carry on until then. As long as you can stay for the full length of one mission (usually about 20-30 minutes, very rarely 40-50), it's fine to join in after we've already started up til probably 9:30.
"It is necessary to develop a strategy that utilizes all the physical conditions and elements that are directly at hand. The best strategy relies upon an unlimited set of responses."
-- Ueshiba Morihei