iOS 10 doesn't seem offer a built-in Contacts whitelist feature, but iOS does expose an API allowing third-party applications to filter-out incoming calls and messages: https://support.apple.com/en-us/HT207099 - someone could easily write an app that would use your Contacts as a whitelist, assuming one doesn't already exist.
For iOS, i leave DND mode on full time. Contacts that are Favorited are serve as the whitelist, are not screened by DND. Any second call in 3 minutes will override DND instead of being directed to voicemail.
