By default, when you select "use network time protocol" (or whatever it's called), it does not automatically select a time server for you. It should, even if it's one randomly from the list.
I don't think this can be done bullet-proof, i.e. a random NTP server might not be accessible from the network the machine lives in, resulting in timeouts while booting, error messages plenty and other such fun.
Unless you can give me a bullet-proof method how this can be achieved, I won't do this due to the reasons in comment #1. Closing as NOTABUG.