The undertakings followed an investigation by the FMA, which had concerns about Alcock and Knight's management of investor funds associated with SPI entities.
The regulator said last October that it had concerns about SPI and "apparent failures"to comply with financial reporting requirements, hold investors' subscriptions on trust, repay subscriptions owed to property fund investors and keep them adequately informed about their investments.
While Alcock and Knight agreed to repay the principal by June, $241,394 of the $600,000 was still outstanding come July.
The FMA agreed to extend the deadline to the end of last month and then pushed it out to the middle of August.
That deadline has now been extended once again to mid-October and one investor in SPI-related property syndicates said the FMA appeared "weak and ineffective" for not enforcing the undertakings.
In response, an FMA spokesperson said the regulator believed "good faith efforts are being made to pay the remaining balance".
"The time extension increases the prospect of funds being returned to investors and therefore is in the best interest of investors," an FMA spokeswoman said.
"We have also taken into consideration the views expressed by some investors, that we should give the directors the opportunity to pay rather than take action that might remove the prospect of payment. We have been very clear with the directors that our rights to take strong action are preserved," she said.
In the undertakings, Alcock and Knight also agreed to not act as a director or promoter of a public issuer of securities until October 2019.