C:\Users\<user name>\AppData\Roaming\Adobe\Adobe Media Encoder\5.5\AMEEncodingLog.txt
Make sure that hidden directories and files show up in Explorer.
That folder is empty, does that only show logs for exports using AME, I am doing a non-queued export from Premiere.
I have been looking for that too but was never able to find a log for direct exports. For timing direct exports I use an old fashioned stopwatch.