Section 158BE of the Income-tax Act, 1961, sets the time limits within which the block assessment under Chapter XIV-B must be completed. This section is crucial for ensuring timely assessments following a search and seizure operation. The statutory time frame is two years from the end of the month in which the last of the authorizations for search under section 132 or requisition under section 132A was executed. If the search was conducted after January 1, 1997, the time limit is one year. The burden of proof lies with the tax authorities to complete the assessment within this period, failing which the assessment becomes invalid. This provision is significant as it protects taxpayers from prolonged uncertainty and ensures that the tax authorities act within a reasonable timeframe.