Added in macOS 10.13.4 and iOS 11.3. Would be nice to have built in:

enforcedSoftwareUpdateDelay

Supervised only. This restriction allows the admin to set how many days a software update on the device will be delayed. With this restriction in place, the user will not see a software update until the specified number of days after the software update release date.

The max is 90 days and the default value is 30.

Availability: Available in iOS 11.3 and later and macOS 10.13.4 and later.

Mentioned https://developer.apple.com/library/content/featuredarticles/iPhoneConfigurationProfileRef/Introduction/Introduction.html and ofc here https://simplemdm.com/2018/01/25/apple-ios-11-3-macos-10-13-4-mdm-features/.

Thanks