A:
Your member must be informed of the charges, given time to prepare his defense, and allowed to appear in his defense.
(RONR p. 645.)
A leave of absence means the member is excused from the responsibilities of membership, including, I would think, attendance at his own trial.
If, by "30 day limit to schedule the trial," you mean that within 30 days you must set a date for the trial, it would seem best to set that date sufficiently after the end of his LOA to allow him to prepare his defense.
If, on the other hand, the trial itself must be held before the LOA expires, you have a much more difficult situation.
Would the member have legal grounds to sue the organization if his trial were held during a time when he was excused from responsibilities of membership?
I don't know and will not offer an opinion except to say that if this situation can be avoided, it may be the best course of action.
In any event, I strongly urge those involved in the disciplinary action to read Chapter XX (Section 60), Disciplinary Procedures, in RONR.