Android O Features A Pause Button For System Updates
This is not a new feature on Android, Google Chrome supports it since Chrome 50 and it is extremely helpful for people who are little worried about their internet. This feature can be helpful when your WiFi is slow to download this large OTA but you are leaving the house where there is no WiFi. You'll either have to stay till your download is complete or re-downloading the same portion of the update every night again and again.
However, we didn't see this feature in the recent minor update which was around 50MB, maybe Google thinks that small downloads like shouldn't have this feature. But we saw this for big updates which was sent out to fix the previous one for Nexus devices. This would make sense, stay tuned for more news like this.
Source : Android Police