When I update my website, I can see in access logs, that Google downloads my sitemap within 48 hours. If I use something like this - https://submit-sitemap.com/ - I can see in my logs immediately, that Google has downloaded my sitemap. May I be penalized for pinging Google for pinging them too much?
Why you do this, submit your sitemap to WT and it's good, there is no need to this. Even if you do not the use the sitemap, there is no issue, but content matters so update the content and Google is smart enough to find the new content in the websites.
If you update your XML sitemap - I do not see any harm in informing Google that you updated it - afterall - why else would Google create a specific option for informing them? Note: Of course you should not be "hammering" Google all the time 24/7 with sitemap pings.
In my opinion the result of 48 hours is very good. Why do you want faster? If after 48 hours the pages are not indexed, then you need to look for errors.
Pinging Google will just get them upset. There is a better way. Always set up a Search Console (SC) or Webmaster Tools account for the website. Then submit the xml sitemap there (<crawl><sitemaps>). However, if you then make changes to a PAGE, use the SC Fetch feature (<crawl><Fetch as Google>) to resubmit the PAGE. It usually take about 10 minutes to see the results in the SERPs - Check the Cache. However, Google sets what appears to be a 24 hours limit on doing this again on the PAGE. Other pages are fine.
Yes you can but it is not needed. Use GSC > Sitemap to "resubmit" the sitemaps. This way you get quick results in seconds.
I delete my sitemap and submit a new one every time I make any changes. Also, besides xml I would have a text site map page that is hyperlinked to every individual webpage found on my site. The more ways to get to your site/page/map the better. I should be able to find every single page in the sitemap. Your sitemap can provide content, navigation and link juice for you. People need to be informed about what's on your website at all times. This way makes it simple to do.