My two best Ts had policies of waiting 2-3 months before talking to my former Ts so that they could form opinions for themselves first about me. (In fact when I moved from one of them to the next one, she wouldn't even talk to new T for 3 mos because she wanted new T to form her own opinion before they talked.) These two Ts talked to my previous Ts on the phone for 15-30 minutes, that's it. No notes. This to me is the best.