An IRN can be cancelled on the Invoice Registration Portal within 24 hours of generation.
An e-invoice's IRN can be cancelled on the IRP within 24 hours of the moment it was generated, not 24 hours from the invoice date.
Cancellation is only possible if the goods or services have not moved or been delivered under that invoice; once fulfilment has started, cancellation is not appropriate even
After 24 hours, the IRN cannot be cancelled on the IRP under any circumstance.
Cancelling an e-invoice also cancels the underlying invoice number for GSTR-1 purposes, so the cancelled count in Table 13 must reflect it and the number itself should not be
From IRN generation, which is timestamped to the minute on the IRP.
The full guide has the formats, the deadlines and the worked examples.