We have, with acceptance by the Customer, run two 10 hour shifts documenting the all failures and submitted our findings to our Customer. Make sure your procedure states that you runoff the machine "per the contract" or "per the agreement" or something. Then all you have to do is whatever you've agreed to. You MUST have a waiver or another agreement from the Customer in order for this to fulfill the requirements. It is a gray area, but if you document what you're doing when you deviate from the standard and why you are doing it, it will usually satisfy the auditors. Also, it just makes good business sense to do so.
We have three choices for Dry Run at our company. We have "as agreed to" in the contract, quote or whatever. We have a standard 2 hr. Dry Run. And finally we have QS-9000 TE Supplement 20 hr. Dry Run. If you can get the Customer to agree to something less inhibiting than the continuous 20 hr. Dry Run, DO IT! You will save yourself a lot of headaches and your company a lot of money.
Please understand we choose to use this format at our company because we build custom automated industrial equipment. Ususally we build only one or two machines (if we're fortunate) at any given time that are remotely similar to each other.
Does this help?