We just had an unannounced audit at one of our sites and did not receive the audit plan ahead of time. I reached out to ask about this because we had at all of our previous unannounced audits. I was told the do not need to provide an audit plan ahead of time, they can do so at the beginning of the audit.
I've also found that on most occasions the auditor (and we've dealt with MANY different auditors) very rarely sticks to the plan anyway. This can happen for many reasons such as things are going either better or worse than expected, certain people have a conflict at the "scheduled" time so that section is revisited at another time, or the information in a section was discusses as part of another section so the need to revisit it isn't necessary.
The only thing we've really used the plan for is to schedule when lunch should be brought in and to try to have the various people available when their area is being covered.