The situation is already beyond nipping it in the bud, so to speak. The disorganization in his behavior is likely prompted by a combination of the custody arrangement and the differences in behavior management between the two homes. I'll be frank with you: the type of custody arrangement you currently have is a formula for problems. It involves too many transitons, lack of consistency and routine, compunded by different behavior managemnt practices. The type of shared custody arrangement you have is not appropriate for such a young child. As a rule of thumb, it is better for young children (up to the age of twelve or so) if they go to bed and wake up in the same bed every school day, so to speak. The probate court that approved this arrangement did not help your son. For your part, if you adhere to the guidelines in LynnClark's book SOS Help for Parents you will be rewarded. Continue to use time out, but employ a chair (instead of standing and instead of his room). See sosprograms.com.
Regarding your second question, yes, it would make sense to change the arrangement sooner rather than later. It will afford much more structure and consistency in your son's schedule.
The family history certainly places your son in at at-risk range re: juvenile-onset bipolar disorder. While it is not unheard of, it is not the customary thing to employ medication with such a young child. It is done, but I think you should attempt the non-pharmacological interventions/changes.
Re: the chair, it is not a make-or-break issue but does make a difference. The main problem with sending such young children to their room is that you then have to 'police' it to be sure what they are doing. It's not a sufficiently structured arrangement for young kids.
I will start to employ the chair. I'm not sure, however, what difference that makes. Obviously it does, since you are suggesting it, but I have not thought of how. I also feel the need to mention that Bipolar Disorder runs in my family. I was diagnosed with Bipolar II when I was 12.
His father and I have decided that once school starts (this year) our son will stay with me during the week, and his father's during the weekend. From what you said, it sounds like this will help. Should we start implementing this sooner? Or should I just wait patiently until school starts? Thanks again for the response. I appreciate it so very much.