Thanks for that info, Ian.
I suppose it would also be helpful to know exactly how long this period of hospitalization lasted. Are we assuming it was a month? Also, what was the nature of his treatment?
If he was hospitalized for a "nervous breakdown" which has been reported as the cause, the length of hospitalization would depend on Brian's recovery from the initial meltdown - but usually as soon as a patient appears better and is not a danger to himself or others he would be discharged for outpatient treatment. I would think 2-4 weeks at the maximum.
Which means the hospitalization could have occurred at the end of June (giving 2-3 weeks before the July 17th appearance) or in October after the Time to Get Alone session, or in August. Peter Reum has stated it was after Friends but we don't the source of that information or if that was a generalization and not meant to be an exact date (as all of the above dates are "after Friends").