It is on account and cos (and please don't modify that zimbra-attrs.xml file, all bets are off if you do):
So the command line would be:
$ grep CacheDuration /opt/zimbra/conf/attrs/zimbra-attrs.xml
<attr id="386" name="zimbraPrefOutOfOfficeCacheDuration" type="duration" cardinality="single" optionalIn="account,cos" flags="domainAdminModifiable">
for one day. The duration syntax is:
zmprov ma user@domain zimbraPrefOutOfOfficeCacheDuration 1d
duration: ^\d+[hmsd]?$. If [hmsd] is not specified, the default is milliseconds.