Chunks' default behavior is to memoize everything on a two hour refresh. If you want to update it on a more frequent interval, you should be able to do this by setting parameters in your parameters/ad.tcl The following should set chunks to expire information once it is an hour old.
ns_section ns/server/${server}/acs/chunks
ns_param newscachelength 3600
ns_param bboardcachelength 3600
ns_param eventscachelength 3600
ns_param classifiedscachelength 3600
ns_param auctionscachelength 3600
