Part of the process of putting a new site live can be moving DNS entries around. Prior to doing this it's a really good idea to sort out the Time To Live (TTL) of the DNS record so that when you do change DNS entries you aren't waiting around for a day for the DNS to sort itself out. Most DNS registrars will allow you to set your TTL down to a minute or so.
It's also very important to check the status of your DNS records to ensure that they have the correct TTL, usually a day before (and day of) the move.
You can check the TTL value of your A record with the host command. Change the value of the -t (type) flag to aaaa or cname to inspect different types of records.
host -a -t a www.hashbangcode.com
This will produce the following output. The TTL of the domain below is '125'.