[wagglebee]

From the article you linked:

What is an adequate observation period to ensure that cessation of neurologic function is permanent?

Recommendations for the length of observation periods have varied extensively throughout the world and the United States. There are no detailed studies on serial examinations in adult patients who have been declared brain dead.

Conclusion.

There is insufficient evidence to determine the minimally acceptable observation period to ensure that neurologic functions have ceased irreversibly.

[sometime lurker]

You are correct that they do not yet have evidence to recommend a minimum observation period. That does not invalidate the guidelines of the 1995 practice parameter.