The expression 'casual vacancy' has not been defined in the Companies Act, 1956. Simply stated, a casual vacancy in the office of an auditor means a vacancy caused in the office of an auditor by his death, disqualification, resignation, etc. It has been held in the case of the Institute of Chartered Accountants of India v Jnanendranath Saikia (1955) 25 Comp Cas 53, 56 (Assam) that casual vacancy is not a vacancy created by any deliberate omission on the part of the company to appoint an auditor at its annual general meeting.
Where the casual vacancy is caused by resignation of an auditor, the Board cannot fill up the casual vacancy but place the matter before the company in the extraordinary general meeting for appointing an auditor in respect of the casual vacancy.
The time limit is not specified for that but before the start of AGM, the auditor should be appointed.