The time you are referring to is the Entry date which you'll find on the Add Weblog Entry form which you filled in to create the post (and also if you click the Edit button for the post). This is set to the current time when you start writing the entry, not when you post it.
If this is unclear you could try having a read of the Noticeboad and Weblog help page in the documentation.
So for your second question "how does that relate to the time I posted" the answer is "it doesn't".
