I noticed that the time recorded when certain tasks are performed are logged with time offset. Yesterday I rebuilt the thumbnails for forum posts. I then went to the Logs > Admin logs in ACP and noticed that it said I performed the thumbnail cleaning at:
All thumbnails matching your criteria have been rebuilt 29 july 2010 - 20:25
But I did the actual rebuild yesterday at 13:25 local board time, which I know as I specifically ran it and then posted in a topic about this.
Note: The time recorded seems to be correct for most other tasks, such as making a change to a forum category.