You can find the requirement in your associations’s by-laws and governing documents. Typically an audit is done annually in the first quarter after the year to be audited. However, some associations have lesser requirements and do reviews, compilations, or none of the above.
For large associations most experts recommend doing an audit every year. Annual audits can catch small problems before they become large and expensive ones to resolve. Another benefit is that audits provide board members and association managers with better information that can be used for budgeting, which can greatly impact financial decisions, such as determining fess and regular assessments.
For additional information about Reviews and Audits, read this article.