Group members may be late sometime. If it's not a usual occurrence, don't disrupt the meeting to review what happened prior to their arrival, unless they are key figures in your meeting. Let the latecomer sit quietly without participating for a while to "catch up" with meeting content. The Facilitator should supply the latecomer with an agenda, plus any supplies handed out earlier. If the lateness is chronic, you could try humor by saying, "Sorry, we must have started early." You might also stop the meeting until the latecomer is seated.
Early leavers tend to drain the energy from a meeting. When people leave, others wonder why the meeting continues. When you review the agenda, point out the ending time and ask if anyone has a problem with that. Those with legitimate excuses will usually state them. Courtesy calls for early leavers to speak with you prior to the meeting to apprise you of their need to leave early. You can then work that into your general meeting introduction, so that other participants will be expecting that. If the early leaver will miss an important feature of your meeting which you can't speed up, you should make this clear. They may decide to stay!