Keeping time on Xen Linodes

I noticed today that /proc/sys/xen/independentwallclock is set to 0 indicating that the domU uses the hypervisor's clock. As I understand it, this means that Xen will keep my domU within /proc/sys/xen/permittedclockjitter milliseconds of the hypervisor clock. I also noticed that permittedclock_jitter is set to 10000000ms which is 2+ hours.

Is the value of permittedclockjitter controlled by the domU config? If so, is their a reason Linode has chosen to set this value so high? Is there any harm to setting this to something more reasonable like 1-5 minutes?

Also I assume that dom0 on each server is running ntp to keep the hypervisor clock in sync?