(DOCSP-6338): Add NTP note.

Author: Tony Sansone

conf.py

@@ -158,6 +158,7 @@
     '.. |onprem| replace:: Ops Manager',
     '.. |onprem-link| replace:: :opsmgr:`Ops Manager </>`',
     '.. |nfs| replace:: :abbr:`NFS (Network File System)`',
+    '.. |ntp| replace:: :abbr:`NTP (Network Time Protocol)`',
     '.. |nvme-clusters| replace:: clusters with local NVMe SSDs',
     '.. |pit| replace:: :abbr:`PIT (Point in Time)`',
     '.. |piv| replace:: :abbr:`PIV (Personal Identity Verification)`',

source/tutorial/install-k8s-operator.txt

@@ -48,6 +48,20 @@ To install the MongoDB |k8s-op-short|, you must:
    If you need a |k8s| solution, see the |k8s|
    :k8sdocs:`documentation on picking the right solution </setup/pick-right-solution/>`.
 
+#. Have a running |onprem-link|.
+
+   .. important::
+
+      Your |onprem| installation must run an active |ntp| service. If
+      the |onprem| host's clock falls out of sync, that host can't
+      communicate with the |k8s-op-short|.
+
+      To learn how to check your |ntp| service for your Ops Manager
+      host, see the documentation for
+      `Ubuntu <https://help.ubuntu.com/lts/serverguide/NTP.html>`__ or
+      `RHEL <https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/system_administrators_guide/s1-checking_the_status_of_ntp>`__.
+
+
 #. Clone the :gh:`MongoDB Enterprise Kubernetes Operator repository </mongodb/mongodb-enterprise-kubernetes>`.
 
    .. code-block:: sh