L.C.
I've not heard of time in, but when my two picked at each other, I put them at the dining room table with a puzzle which they had to do together without talking for 15 min.... Or I put them in a room together with a pile of legos and told them they had to sit together, but they couldn't talk for 15 min. You'd be amazed at how they banded together in silence. :-)
Once in a while I told them they had to sit together with an activity or a game that required oral communication, but they weren't allowed to fight. They had to play the game and follow the rules.
Usually when the 15 min. were up, they wanted to continue with the activity...
YMMV
LBC