If you don’t want people to be able to detect your rough geographic location, you should be using a proxy to hide it. For everybody else, knowing the edge server you are closest to is really not a threat.
If wishes had wings, sheep would fly. People who want their computer to do a certain thing can also be expected to do a quick web search for how to make it do said thing. E.g.: hiding location? Use onion routing. Signal doesn't claim to hide your country (heck, they require your phone number!) so it seems wishful thinking to say they should have included e.g. a Tor client and enabled it by default
The same information would then be available in the timing, but given the distributed nature here, that would be a lot harder to pull off.