dnscontrol/documentation/functions/domain/NAMESERVER_TTL.md

name	parameters	parameter_types
NAMESERVER_TTL	ttl	ttl target modifiers... Duration string RecordModifier[]

TTL sets the TTL on the domain apex NS RRs defined by NAMESERVER.

The value can be an integer or a string. See TTL for examples.

D('example.com', REGISTRAR, DnsProvider('R53'),
  NAMESERVER_TTL('2d'),
  NAMESERVER('ns')
);