Eu entendi que, se suas VMs forem ativadas e desativadas com frequência (como no escalonamento automático), o chronyd é o melhor serviço:
If your computer is connected to the Internet only for few minutes at a time, the network connection is often congested, you turn your computer off or suspend it frequently, the clock is not very stable (e.g. there are rapid changes in the temperature or it’s a virtual machine), or you want to use NTP on an isolated network with no hardware reference clocks in sight, chrony will probably work much better for you.
Se estiver sempre ligado, então ntpd, como Paulo menciona.