There is an on going issue with Geocaching.com logs dates. For more information see this post. Groundspeak are aware of this long time problem but as yet haven't implemented a fix.
In an effort to get GSAK dates to match those shown on the Groundspeak server I have implemented my own fix and you turn it on by checking this box (the default)
Basically, the idea of the fix is to make all log dates line up with what shows on the Groundspeak server when you look at a cache.
However, this is a "virtual" fix as the date in the logs table is not actually updated.
When this option is selected (default), all references to the ldate field in the logs table, effectively uses the function g_GcDate(ldate,ltime).
This means that the logs table remains unchanged. However, the Caches table contains 3 fields which are dependent on this date, and hence they need to be recalculated if this option is changed (which will happen on every database you open after installing V8). The 3 fields are:
1. FoundByMe date
2. LastLog date
3. Dnf date
Macro authors can test the system variable $_GcCorrect to determine if the user has this option selected or not.