lammert - 7:43 am on Jun 23, 2010 (gmt 0)
The TTL times are in the DNS record settings. You could either see them in the DNS server configuration file/panel, or on your local computer.
If you have access to a Windows computer, open a command prompt and type the following command:
Inside the nslookup program, type the following three commands:
This will show you the currently distributed MX records together with the TTL times assigned. The nslookup command is also available under Linux, but it doesn't seem to tell you the TTL times in debug mode.