The server communicating by RFC 2616 must provide its time information to the contact person. The server obtains and displays time information after accessing the site.

A server with a lot of load goes slowly little by little. Generally, it is within milliseconds, but if accumulated, it may differ from standard time by several tens of seconds.
The server administrator should periodically check the server time to match the standard time. However, in systems where time order is important, it is recommended that you set up and calibrate a separate check period because sudden server time correction will cause the server to time back or time back.