Hi Corporal_hick
There is no way to tell XSI to keep the rendering window open if you render inside XSI's gui. There are options with command line rendering that allows that, I suggest you read the Standalones Manual to learn more about this.
For your first question, there are two things that you need to do to get the rendering time.
1-In the Render options, go in the Message tab, and check Progress report. You can use Verbose, but this will spit tons of informations about the rendering, while you only need the basic infos. The Progress report option will give you informations during the rendering about what is happening under the hood. At the very end of the frame you get the time it took to render the image.
Note that the progress report can be read on the bottom bar (at the left) or in the script editor.
2-To output this information to a text file, you must go in the user preferences, Scripting tab, and there you have options for the script editor and to save its content to file.
Hope this helps
Salutations - Cheers
Bernard Lebel