r00xxbr Since the time request is a "system service," it doesn't go through the app's VPN tunnel.
discuss.grapheneos.org
That is not true in general. For example, as documented on the GrapheneOS web site, some connectivity checks detour around VPN tunnels, so that the OS can detect when the VPN is trying to run through a captive portal before the user has logged in / agreed, and being squashed. "Wi-Fi calling" aka VoWiFi, always runs outside VPN tunnels. Because the claim is not true in general, whether or not it is true for this case should be checked.
As a citation, "discuss.grapheneos.org" is not of high quality, because it doesn't allow the reader to examine the underlying evidence (this is what citations are for). Please provide a link to one or more particular threads on the web site. This is the best practice even if (hypothetically) one is consulting an LLM that doesn't provide direct links (for example, ask the LLM to provide direct links, and then click on them to make sure they're accurate).
Finally, as other8026 suggests, since this issue is not widely reported, it seems plausible that the problem may be due to a particular VPN client or configuration. Perhaps somebody's "ad blocker" is falsely implicating time.grapheneos.org?