"It was just how we would work it in with our finances."
The foundation's $1 million donation will be paid over three financial years from 2016-2019, and Ms Teki-Clark said the Sarjeant's redevelopment project would strengthen and restore the existing building in Queen's Park and add a new purpose-built wing.
The Sarjeant Gallery Trust already has more than $22 million in cash and written pledges, Ms Williams said, but the written pledges would need to be finalised to match the $10 million in Government funding.
The $22 million includes $5 million from Whanganui District Council, while the $10 million needed to match the government contribution must come from independent sources and the council's money cannot be part of it.
The end of June funding deadline is crucial, Ms Williams said, because it has already been extended twice and Arts, Culture and Heritage Minister Maggie Barry might not extend it again.
Ms Williams is determined to meet the deadline, and said the building project could begin as early as mid-2017.