If Mojave doesn't include ntpd, how do Mojave systems keep time in sync?

NTP has been victim to some exploits and it maybe that Apple have chosen to throw out NTP because of this. As per the article kindly linked to by dialabrain Apple now use 'timed' as an NTP client, again as per that article this is not the standard timed software but a heavily customised version with no options. I have not found any indication it can be used as a corresponding equivalent NTP server. I did find one post which suggested one person had seen a message requesting permission to allow incoming traffic for timed, this implies it might be wanting to act as a server under some unknown circumstances.

Now whilst Apple's continuing efforts to improve security for macOS are important and desirable it is increasingly looking like Apple are choosing to throw out the children with the bath water. :( Whilst Apple have effectively abandoned even their feeble Server.app as a server it allegedly is still an official 'server' for OpenDirectory. All directory servers including OpenDirectory require the server(s) and client(s) have their clocks in reasonably close synchronisation, this is normally done by making the directory server(s) also NTP servers and getting client(s) to sync their clocks to the servers. This is how Active Directory works and historically when a Mac was setup as an OpenDirectory server it also automatically became an NTP server with OpenDirectory master and replica servers syncing between themselves.

Apple cannot be bothered to tell people about most of these changes so we do not know for certain all that has changed but it does sound like there may be no NTP server capability - not even a hidden one using some unknown software. :(

Other than admitting defeat and totally giving up on Macs as servers even for something as 'trivial' as NTP your best bet is to find some open source equivalent and run it on the Mac, theoretically this could even be the 'real' NTP software. Personally I loooooong ago gave up and switched to using Linux VMs for all server functions.

Not that it helps but it seems Mojave still includes SNTP.

Apple do operate their own NTP servers and these are the ones listed as standard in System Preferences -> Date & Time. It would seem Apple expect all mac 'Servers' and clients to all go out across the Internet for time synchronisation. This would work but is not the way the overwhelming majority of larger organisations work.

Apart from relying on -

1. Apple's servers rather than your own or even your own NTP/GPS/Atomic signal
2. A working Internet link (some networks are even deliberately disconnected from the Internet - aka 'Air gapping' for even high security)
3. There is also the extra Internet traffic and latency

It should be noted that the 'removal' of NTP was not listed in this document - https://support.apple.com/en-gb/HT208312

However arguably (but not helpfully) NTP was not part of Server.app itself so strictly speaking this is not misleading.

See if this page helps: https://apple.stackexchange.com/questions/343889/how-do-i-enable-ntpd-to-serve-ntp-clients-using-macos-10-14-mojave