It seems that currently it is not possible to accurately obtain the exact timestamp (with milliseconds) of the time a request was sent to the server. This is important for many usecases where it is necessary to analyze based on the exact timestamp an actual request was issued to the server.
The timeline details provides a "rough idea" of when approximately the request was sent by marking it on timeline. However, it is quite difficult to obtain the timestamp based on just this information as there is no absolute reference and exact deviation from this reference.
The information saved by "Save as HAR with content" option provides a start timestamp - implying this information is indeed managed by devtool but is not readily made available in the user interface. Can you please provide an option to obtain the absolute timestamp details of a message, preferably alongside the message details that appears in the attached screen-shot.