The TTL heading stands for Time To Live and is refferring to the Domain Name System (DNS), the TTL is set by an authoratative nameserver for a particular resource record. Basically the Time To Live determines how often the Blacklist Tool will check that particular blacklist.
Keep in mind that the time It is listed in seconds, so 3600 seconds is an hour.
Thank you,
Wendy
Wendy
MXToolBox Support
support@mxtoolbox.com