Advance tax instalment timing clarified: payments due on or before prescribed dates in equal instalments aligning with the statutory schedule. Amendment revises timing language for advance tax by replacing 'before the date' with 'on or before the date' across subsections and prescribes that payments corresponding to a declared statement be made in equal instalments on dates applicable under the statutory schedule, while payments based on an estimate be made in equal instalments on remaining applicable dates or in one sum if only the final date remains.