$TTL strange comportment with 8.2.3

[maurywind at interfree.it]

Dear all,
I've some problem with $TTL statements into BIND 8.2.3.
Infact though i write (into first line of my dbs) the $TTL 10800 (or 3h), this server (it's my primary-master) after 1 day, erase this $TTL statement and my secondary 9.2.1 to see me that $TTL is not 10800 as i have wrote both servers but is 86400 !!
Wath is its reason ??
My problem is that my network-structure (intranet) must have a little time for negative caching, for us it's reasonable about  3 hours !!
Can you help me ??
Many thanks
Maurizio

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