Comment 4 for bug 1933828

The server is set via a configuration file. The default config file is /etc/systemd/timesyncd.conf and it can be overridden by dropping files in /etc/systemd/timesyncd.conf.d/.
There is a pool of free ntp servers available on https://www.ntppool.org/en/.

To test this fix you also need a DHCP server that returns NTP records.

With VMs, you can use dnsmasq to provide NTP records by changing the values in dnsmasq.conf
# Set the NTP time server addresses to 192.168.0.4 and 10.10.0.5
#dhcp-option=option:ntp-server,192.168.0.4,10.10.0.5

Or if you're using libvirt, edit the configuration with "virsh net-edit default" (or the name of the network your VMs are attached to) then pass the option directly to dnsmasq (cf https://libvirt.org/formatnetwork.html for reference)