@Pettefar 

Hi，thanks for posting question here.

System time is the router's current time displayed. The Router's system time will be referred when you use the time-related features on the Router, such as Wireless Schedule and Parental Controls.

There are two methods to configure system time:

    1. Using the Web management interface, please go to Advanced > System Tools > Time Settings.

    2. Using the Tether App, please open Tether App and go to "Tools > System Time" or "Tools > System > System Time".

Once you are in, you may choose to "get time from Internet automatically" or "manually specify the time".

Additionally, here are some tips for you if your router fails to get correct time from Internet:

    1. Check if DayLight Saving Time settings are correct.

    2. Make sure your PC is able to get time from the Internet correctly when connected to the Router network, you may have to contact your ISP if the PC doesn't work as well.

    3. Go to time settings page of the Router > manually enter custom NTP servers in the NTP Server field, such as time.windows.com or time.apple.com
How to set up System Time of the Wi-Fi Routers

  @Pettefar 

If you've meant the system uptime, this may have not been implemented - not all router models have this feature - check this feature request for example.