Just to add a little bit, aging and scavenging can used to perform this
function. It need to be turn on in two places. Open up the MMC for DNS,
right click you server name, then properties, then go to the Advanced TAB,
at the bottom check "Enable automatic scavenaging of stale records"
Then go to the zone reverse lookup zone and right click, then properties,
bottom right conner.Click aging, then check Scavenage stale rescource
records"
One other point that i must make if you set this the current records in
there will not be effected. So you will either have to remove them and then
let the clients register. Then these new records will have the correct time
stamp on them.