I didn't count exactly but I recreated your experiance using a golem (to see if it was inherently a golem) and the equipment provided (interesting) and placed a variety of units on that same command structure as well as having a caster chain fatigue himself out without troops.

Someone with some paitence could try to find the exact limit with testing phases, easiest way to do this is to have an army on 1 side with 1 Master of the Dead, 1 other Commander with "Hold, Hold, Hold, Hold, Hold, Retreat" with 1 unit on guard commander and one on the other side with 1 Priest.

Set them as far apart as possible.

Only research 1 level in Enchantment and as many in construction that you can get some protection items (You don't want these panzies to die)

Put a decent reinvigoration item, or 2 on the Master of the Dead so he can cast every turn without getting in the hole with fatigue. (You can use any mage that can cast undead; but don't research and watch out for national spells they will taint the test)

Set the orders of the Master of the Dead to "Raise Skeleton, Raise Skeleton, Raise Skeleton, Raise Skeleton, Cast Spells" and the Priest to "Banishment, Banishment, Banishment, Banishment, Banishment, Cast Spells"

First turn the Priest will cast Blessing because he can't banish but from that point on they will just stand there, the Master of the Dead summoning and the priest (with protection items) banishing them.

Start counting the rounds after the "other commander" retreats.

Or what would be great would be for someone who knows to post it