Hi Hutch,
I had noticed some date discrepancies on DNN sites. I think the dates are stored in the DB in the same timezone the server is setup with. If you don't control your server, you cannot control much of this. So if you query the DB directly, it will show the date/time as the data was created based on the server timezone.
Now when it displays via DNN it will try to adjust the date/time stored with the same timezone set under Site Settings/Advanced Settings/Security Settings / Timezone. I don't think it does a good job on that.
Bottom line is that I think this is either a bug or just something that I couldn't figure out how it works. I usually just try to have the site timezone and the server timezone set to the same, but I realize this is not always possible, specially for users who host their sites on shared hostings.
Aderson