During that time, they have overwhelmed their followers with photos and updates from some of New Zealand's most scenic spots, including The Remarkables, Lake Hawea and Amisfield Winery.
Witherspoon's Instagram posts have gone out to more than 8.6 million people, while Oprah is just behind on 8.4 million followers.
Comedian Kaling also holds considerable sway, with 2.5 million followers.
It's not clear whether Winfrey, one of the most famous people in the world, or Kaling - star of hit TV series The Mindy Project - are leaving at the same time as Witherspoon.
The stars' effusive and unrelenting praise for the their time in Aotearoa has lead to rumours of some sort of promotional agreement.
But the New Zealand Film Commission has denied any kind of deal to have the likes of Witherspoon and Winfrey gush about the country, telling the Herald there's "no partnership or relationship of any sort".
A representative for the NZFC said the production may receive a screen production grant from the Government, if it qualifies once filming is complete. Under the scheme, international productions can qualify for a 20 per cent cash rebate of their New Zealand expenditure, if they spend more than $15 million while filming here.
The movie has an estimated budget of $144m. A Formal application for the grant can't be made until filming is complete.
Directed by Ava DuVernay, A Wrinkle in Time is slated for release in 2018.
The film is based on the popular children's book by author Madeleine L'Engle, originally published in 1962.
Other big names cast in the film include Chris Pine, Zach Galifianakis, Storm Reid and Rowan Blanchard.
