Manually activate site map generation?

I've been trying to set my setting to yes in the site map file generation but it times out when I push submit.  The files got deleted and I am wondering with that no glowing red if they will regenerate tonight with the check box checked "enable site map generation" 

If not how can I manually turn that to red?  Or does it do that when it generates it tonight?  Is that also nightly?  

If site is considerably big then sitemap generation can take some time - as the result live generation from admin panel could fail, but sitemap is generated on cron (every day) - and it should generated there without problems, since there is no timeout there.

The other question I have is once something is generated in the site map, if it is deleted in database will it be deleted in the site map?  Or is that something that must be done manually?  If you have multiple deletions and or corrections to uri's is it best to just delete the old files and let the site regenerate the files?  

I forgot the city in 100's of uploaded files in the URI.  The site map was generated then I went back to correct the URI's by adding the city.  Well Google is like these url's do not exist and of course they don't because I manually fix them.  Going in and finding 100's in 500,000 is not my idea of let's do it. The site map in this case is not going to delete or correct those old files will they?  So really it is find them delete them or start from scratch and let the system redo the site maps correctly by just deleting the old files? Do I have that right?  Seems more efficient to me to just delete the old?  Am I missing anything here? 

They were rewritten and what I thought is indeed correct...

 You are correct.

You don't need to do anything, upon next sitemap generation(once a day by defult) all site urls are re-added from the scratch.