masscan with the right setup (namely hardware + drivers but also connection obviously) can scan the entire IPv4 space (+ all ports) in ~5 minutes.

Source Code: https://github.com/robertdavidgraham/masscan

Article from PoC || GTFO with more internal details on how it works: https://www.alchemistowl.org/pocorgtfo/pocorgtfo15.pdf (Page 66) [Note: PDF is both a valid PDF + valid ZIP file with source code]

That depends on the machine you are using. Tools like mass scan to locate open ssh ports and then testing them doesn’t need to take long if you have a beefy machine and pipe to the internet.

~4 hours on a 1G port, IIRC

I’m sure you could do it a lot faster with a better CPU and 20% commit on a 10G port