It is expected that Apple will release a Big Sur update soon. RC or public version is expected on November 10th. Is Norton ready? Kaspersky recently made an update to Big Sur support, but there is no news that Norton is ready yet.
When I upgraded to Big Sur, when I restarted, Norton couldn't complete setup and errored out and after another restart it deleted itself. I downloaded the installer and it all seems ok upto when I have to restart the mac to finish setup and it throws up a big error and deletes itself? any ideas? - Macbook Pro 16" 2019 model
Your idea of 2020-Nov-12Th is a good way, but this is not all.
But before, you have to know that OS 11 Big Sur, although of slightly more than 12 Go, indeed needs 35.5 Go of free disk space, (if your click on "More informations" just before the upgrade, you are redirected on the Apple web-site corresponding page, and it says that).
Free some space until at least 35.5 Go, occasionally update the slightly more than 11 Go XCode (which also required more), still keep a look at your 35.5 Go free space.