Redirect index.html to index.php

I have never edited a .htaccess page before, but I would like to add a redirect from my old index.html to my new index.php page.

I have added a redirect in HTML, but even though I made the redirect time 0-seconds, the redirect is still taking about 1-second. (The time is not a big concern, but it does flash a blank white page for that second, and I would prefer it didn't do that).

After reading some different information on the internet it looks like I should be adding this to the first line of my .htaccess
I made this change, but it did not affect anything. I called my hosting service and confirmed which .htaccess file I should change, and they confirmed that it is the one in the public_html folder.

Questions:
1. Do I need to delete the index.html file for this to work properly? I would have thought that the above code would not even execute the index.html file?
2. Am I making this change in the correct area? (The .htaccess file under the public_html folder).
3. Is there different code that I should be using?
4. Will making this change, affect my rankings on web search engines? (If I skip the .htaccess redirect, and just rely on the html redirect, will this also affect my rankings on search engines?)

Thank you.