Normally the audit plan is a required part of the last audit report, so clients have it anywhere from 6 months to a year in advance.
A 3 year audit program is required to be part of a reassesment report whenever one of those is done and it provides 3 years worth of future planning barring any need for change that could be caused for a variety of reasons.
Regardless, every audit (surveillance or reassessment according to ISO 17021) has to address the following:
a) internal audits and management review,
b) a review of actions taken on nonconformities identified during the previous audit,
c) treatment of complaints,
d) effectiveness of the management system with regard to achieving the certified client's objectives,
e) progress of planned activities aimed at continual improvement,
f) continuing operational control,
g) review of any changes, and
h) use of marks and/or any other reference to certification.