highly recommend it. some groups use a timer. My home group found that a little "insensitive" to the new ppl.
Home group members and the ppl they sponsor pass the word that it's 2 or 3 min per person as a rule. Table leaders then inform their tables, based upon how many ppl are there, roughly how long each person has to talk if everyone is to share (we break into tables of 5 to 15 ppl per rather than staying in one large group). Table leaders are responsible to make sure their tables end at the appropriate time so we can do a group prayer. If the table isn't finished, they're welcome to go back to sharing after the prayer.
Brand new ppl are given some slack - they probably haven't learned the deal yet so if it's the first or second meeting for them, we typically let them talk. Of course, if it get too crazy, its the duty of the table leader to gently stop them and offer to speak to the person after the meeting.
My great grand-sponsor had 55 years and I never heard him share for over 4 minutes.... maaaaaaaaaaaaaybe 5. He always used to say, "The Gettysburg address was said in less than 5 minutes - who are we to think that what we share at a meeting is MORE important than one one of the most famous speeches in history?"