Смещение (t) для локальных часов расчитывается по формуле:
Timestamp Name ID When Generated
------------------------------------------------------------
Originate Timestamp T1 time request sent by client
Receive Timestamp T2 time request received by server
Transmit Timestamp T3 time reply sent by server
Destination Timestamp T4 time reply received by client
The roundtrip delay d and system clock offset t are defined as:
d = (T4 - T1) - (T3 - T2)
t = ((T2 - T1) + (T3 - T4)) / 2.
Источник:
https://datatracker.ietf.org/doc/html/rfc4330#section-5 
