When I hit the nginx server with a very rapid succession of requests from multiple clients, the logs will be out of order. For example, the log times would appear like this:

... 18:10:11 ...
... 18:10:11 ...
... 18:10:11 ...
... 18:10:12 ...
... 18:10:11 ...
... 18:10:12 ...
... 18:10:11 ...
... 18:10:12 ...
... 18:10:12 ...
... 18:10:12 ...

Why would this be?