The use of different Time To Live fields with in a RRset have been deprecated and this is enforced by the server when loading a primary zone. See the Security section for more discussion of differing TTLs.
The Time To Live assigned to the records and to the zone via the Minimum field in the SOA record is very important. High values will lead to lower BIND network traffic and faster response time. Lower values will tend to generate lots of requests but will allow faster propagation of changes.
Only changes and deletions from the zone are affected by the TTLs. Additions propagate according to the Refresh value in the SOA.
Experience has shown that sites use default TTLs for their zones varying from around 0.5 day to around 7 days. You may wish to consider boosting the default TTL shown in former versions of this guide from one day (86400 seconds) to three days (259200 seconds). This will drastically reduce the number of requests made to your name servers.
If you need fast propagation of changes and deletions, it might be wise to reduce the Minimum field a few days before the change, then do the modification itself and augment the TTL to its former value.
If you know that your zone is pretty stable (you mainly add new records without deleting or changing old ones) then you may even wish to consider a TTL higher than three days.
Note that in any case, it makes no sense to have records with a TTL below the SOA Refresh delay, as Delay is the time required for secondaries to get a copy of the newly modified zone.