Up to the minute, more or less
Google puts a time stamp on every message it displays and every message it archives. The time stamp indicates the date and time (in Pacific U.S. time, regardless of where you’re located) when the message traveled through Usenet and hit Google’s newsgroup server.
Keep in mind that time stamps for the same message differ from server to server. Also, Google has a reputation for being slower than ISP (Internet service provider) servers. Since the great overhaul of Google Groups, I have monitored latency (which means the time delay between posting a message and seeing it appear in Google Groups) with uneven but improving results. When this beta test was first launched, the latency was a disastrous nine-teen hours according to my testing, which compared selected newsgroups both in Google Groups and in a dedicated newsgroup reader. (That reader accessed the newsgroup server of a large national Internet service provider.) Since then, Google has really snapped to it, dramatically improving server performance. Delays are measured in minutes now, not hours.