What is timedatectl's definition of "synchronized"?

timedatectl produces the following output:

Local time: Tue 2022-05-10 01:07:46 UTC
           Universal time: Tue 2022-05-10 01:07:46 UTC
                 RTC time: Tue 2022-05-10 01:07:46    
                Time zone: Etc/UTC (UTC, +0000)       
System clock synchronized: yes                        
              NTP service: active                     
          RTC in local TZ: no

I see that the system clock is synchronized with NTP, but how synchronized is "synchronized"? How frequently is NTP consulted, and if the connection to the NTP server is lost, at what point will the system decide that the clock is no longer in sync?