Default TTLs in Windows DNS
It appears that the Minimum Default TTL in the SOA is how long failed DNS queries are cached, as Celada stated.
The 20 minute TTL on each record is independent of that, and is set by the client when dynamically updating its own record (the default is 20 minutes).
The default of 20 minutes can be changed by setting a DWORD named
HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters (the value should be in seconds. A reboot is not necessary for it to go into effect, but you'll need to run
ipconfig /registerdns after the change if you want the new TTL updated immediately.