This specifies how far back the logs should be processed <b>the first time</b> the cronjob wants to process statistics. If you have a lot of traffic and are on shared hosting, it's probably not a good idea to go too far back, as it could take a long time to run and be quite resource intensive. (Note that for this setting, 1 month = 28 days. In the graphs and reports generated, 1 month = 1 calendar month.)