TTL

 TTL  is Time-To-Live, a measure in seconds of how long a DNS record (such as a name-to-address mapping) is valid.

How to configure
You may want to reduce your TTL on your domain names to a very low value when preparing for a site migration from one webhost to another.

E.g. on Directnic.com,
 * Find your domain ("My Services" menu, "Domains" item, search for your domain by name, click on it)
 * Select the DNS: Manage button
 * Scroll to the bottom to DNS Time To Live Value
 * Set the number to as low as you can (600 was the minimum as of 2019-02-24)

DNS Examples

 * Google's public DNS at 8.8.8.8/8.8.4.4 respects TTL settings as low as 0, effectively supporting a setting for 'do-not-cache'.
 * OpenDNS's public DNS at 208.67.222.222/208.67.222.220 has a minimum TTL setting of about 10 seconds.

Observing the Effect of DNS TTL
On a terminal with the dig and watch programs, run a per-second lookup of the domain under test:

watch -n 1 "dig +short test1.indieweb.org @208.67.222.222"

As you then update DNS IP settings, the results displayed should change to the new IP setting within the seconds specified in the TTL.