Fastest DNS Propagation Ever!

How about instantly? I'm changing the email address for a ministry and so last night I logged into the Customer Area of 1&1's website, created the new domain, a new subdomain for mail and pointed the subdomain's A record to the customer's public IP address. This morning I went to check the parent domain's MX records and nothing had changed. Hmmmm - Oh MAN! I could have kicked myself because I forgot to point the parent domain's MX record to the subdomain. I thought, "Great! Now I'll have to wait until the next day for this change to take effect." However, I decided to do an NSLOOKUP immediately after I had hit the 'Submit' button y'know, just in case. To my shock, I saw that the MX record for the domain had changed!! I logged into the customer's site and used their name servers to check and sure enough, it had changed there too. Still not believing, I hit three different DNS checking websites and they all confirmed that the change had taken effect. Still, I'll wait until tomorrow before I change the customer's Exchange server to make the new domain the primary address.