Most law firms in NSW, advocate that the time limitation of 6 years is enacted upon the date of breach (wrongful denial of liability).
For example, your total disablement is 19 May 2013, but submit a TPD claim on 19 May 2015 and declined on 1 December 2015. Most people would think you would have until the 1 December 2021, to commence proceedings.
However, the case of Globe Church Inc v Allianz Insurance Australia Ltd  NSWCA 27, and by a narrow 3:2 majority has adopted the approach in WA & Tasmania, namely, limitation period runs from the occurrence of the insured event (eg total disablement) rather than from the date of breach (wrongful denial of liability).
Relating to the example above, it would mean the 6 year time limitation is 19 May 2019.
This is an important case for TPD practitioners commencing proceedings in the NSW jurisdiction.
A diligent TPD Lawyer should be able to give strategic advice to your client’s rights. The case is linked here https://www.caselaw.nsw.gov.au/decision/5c6f3296e4b02a5a800beb5f