BSA chief executive Belinda Moffat said television provided the community with "a rich source of information and entertainment".
"It's particularly important in our current environment," she said.
"But we want our viewers, especially our tamariki, to be safe. Broadcasting standards provide protections to keep audiences safe, and these changes are part of that."
Programmes rated 18 and over can only be shown after 9.30pm.
Programmes rated M can play during school hours, between 9am and 3pm during the week, and after 7.30pm any day.
On weekends, public holidays and school holidays, no M-rated content can play until 7.30pm.
More information can be found by visiting the BSA's www.safeviewing.co.nz website.