Time limit for notice: reopening allowed beyond three years only where evidence shows substantial escaped income. The amendment replaces the time-limit rule for issuing notices under section 148: notices are barred after three years unless an extended-window condition applies; reopening between three and ten years is allowed only if the Assessing Officer has books, documents or other evidence showing escaped income represented as an asset amounts to or is likely to amount to fifty lakh rupees or more. Transitional protections prevent issuing notices for years beginning on or before 1 April 2021 where prior time limits already barred them, and periods of showcause responses or court stays are excluded from limitation, with a minimum seven-day extension for subsequent Assessing Officer action.