I started doing the timed puzzles today without problem through the 4x4 and 5x5s. I honestly don't remember if I successfully completed any 6x6, but I do know that I finished a 6x6 only to notice that the time is 0:00. When I went back to the 'getset' page it looked like this:
I've done two more 6x6 with the same result - timer progresses as I work the puzzle but resets to 0 upon completion. I can't select the 8x8 puzzle.
When I go to the overall 6x6 rankings,
http://www.calcudoku.org/ops/timed_rankings/en/world/6, the tables for today's and yesterday's scores do not display but the best time, best three, and best 100 tables do.