As you progress through different strata there are network delays involved that reduce the accuracy of the NTP server in relation to UTC. Timestamps generated by an EndRun Stratum 1 Time Server will typically have 10 microseconds accuracy to UTC. A stratum-2 server will have anywhere from 1/2 to 100 ms accuracy to UTC and each subsequent stratum layer (stratum-3, etc.) will add an additional 1/2-100 ms of inaccuracy.