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Internal audit can be done in any time of the financial year with 2 or 3 months as an interval for reviewing the books of accounts for the previous 2 or 3 months. Concurrent audit is done without intervals like that for daily reviewing of the accounting treatment for check out of stable internal control procedures. A tax auditor can do interim audit but they dont do mostly but for control purpose but usually with an interval only...

To add further, the ICAI has recently imposed restrictions (barred) on appointment of internal auditor as tax auditor of an entity.