A development approval under the Sustainable Planning Act 2009 remains valid until it lapses under section 341, which is generally four years for a material change of use and a reconfiguring involving operational work, and two years for a reconfiguring not involving operational work...unless the approval states a different period. A development approval lapses at the end of its 'relevant period' unless you seek an extension under section 383. There are certain procedural requirements and limitations and it is usually advisable to seek advice well in advance of an approval lapsing.