Keeping the clocks on all server and client machines in your cell synchronized is crucial to several functions, and in particular to the correct operation of AFS's distributed database technology, Ubik. The chapter in the OpenAFS Administration Guide about administering server machines explains how time skew can disturb Ubik's performance and cause service outages in your cell.
Historically, AFS used to distribute its own version of the Network Time Protocol Daemon. Whilst this is still provided for existing sites, we recommend that you configure and install your time service independently of AFS. A reliable timeservice will also be required by your Kerberos realm, and so may already be available at your site.