DNS propagation

[unix at edify.com]

Hi
   I am running my primary DNS using BIND 8.1. This weekend, I am swapping
name, IP address, and role with that of Win 2003 DNS (secy). I would like
these changes to be propagated as quickly as possible to the outside world.
I am presuming that by lowering my TTL, I can ensure this can happen. My SOA
is below. Can someone please advise me how much low can my TTL be?. TIA for
your time.

$TTL    86400
@       IN      SOA     mydns.mydomain.com. root.mydomain.com. (
                        2005041801 ; Serial YYYYMMDD01
                        8000       ; Refresh
                        3000       ; Retry
                        1500000    ; Expire
                        86400 )    ; Minimum TTL
;
Ragu