I've been working on these, and getting a lot of success so far. My table has six players who are good about avoiding tabletalk and distracting behaviour when it's not their turns.

Rule 1: don't split the party.

Rule 2: if you do split the party, try to keep to no more than three groups.

Rule 3: each group gets 2 and a half minutes of time per player per turn. This is shared time, so a group of two gets five minutes to discuss their actions and do things. If I spend a lot of time in descriptions or npc activities, the timer is paused during those gm portions; this doesn't apply to things like reactions to player activities.

Rule 4: if you want to prepare your next move, leave the room to discuss it with the other players in your group

What I've found:

This seems to work quite well actually. It encourages a metagame aspect of trying to keep from going solo... Two and a half minutes is enough to do something, but a bit dissatisfying. Five or more minutes is enough to get stuff done, especially since it's never much more than ten minutes before you go again. This might not work in a less considerate gaming group.

Anyone else have systems for splits?