Here's the checklist I've pretty much been using for 20 years of 3rd party auditing, it's been used for every type of audit I've done for every ISO and other standard I've audited including 9001-14001-45001-50001-BS16001-PAS99-RCMS-RC14001-ANSI Z10. Some might not like it, but accreditation witness auditors have not once had a negative comment.
The opening and closings should not be long, drug out affairs that turn into torture sessions, and in all honesty from what I've experienced, the vast majority of people that show up are either doing so for face time to demonstrate "their interest", because they were instructed to do so to impress the auditor somehow, or as non-contributory strap-hangers who'll have little or no engagement during the audit.
Just do a quick intro of the auditor, maybe a quick blurp about what's going to happen, and then turn it over. Most of the time there is no need for a long, protracted dog & pony show involving a never ending cycle of smoke & mirrors, power points, and speeches. If the opening or closing go beyond 15-30 minutes time has been wasted and you accomplished very little more than an extended meet & greet which has nearly bored most of the parties to death.
Harsh reality.