I've got five groups now; I plan to cut down to three soon, but I 

still need to get them into some sort of linear time.  Nabiki is _way_ 
ahead of everyone else chronologically, while Ryo and Tachi have killed a 
lot of time in their various travels. <<

That would put Nabiki, Ryo and Tachi at roughly the same amount of time spent. Next, no one knows how much time has passed since Ranma and co. began fighting Ryoga or since Spring and Shampoo began searching for the locket. I guess that put everyone's groups at about the same time right now. When the time comes to lump together the groups you wouldn't have any problems!