Here's the full draft in Chinese: http://www.cac.gov.cn/2023-08/02/c_1692541991073784.htm. It's actual 40 minutes for "Under 8" and not 8 minutes. Here's my own summary:
The proposed guidelines do not just affect smartphones, but all mobile smart devices for kids.
The proposed 5 age groups are:
- Under 3
- 3 to under 8
- 8 to under 12
- 12 to under 16
- 16 to under 18
Default time limits are (parents can exempt all time limits):
- under 8: 40 minutes
- 8 to under 16: 1 hour
- 16 to under 18: 2 hours
- Reminder to rest every 30 minutes
- No service to be provided to minors from 10PM to 6AM the next day
Apps not subject to time limits:
- emergency-related (safety, emergency calling etc.)
- approved educational apps
- tools suitable for minors (image processing, calculator, measurement etc.)
- User-defined by parents
Content providers are also required to provide age-based service under "minor mode". You can find the recommendations for different age groups under the heading "五、移动互联网应用程序未成年人模式要求（一）基本要求", it's too long for me to translate.
There's more information in the full draft, this proposed guidelines is basically a mix of parental controls and NSFM (NSFW but for minors, not safe for minors) requirements for content providers.