puzzles

Albert Einstein was standing on the station platform thinking about relativity when he noticed that he could see two station clocks. Each clock was digital, showing only hours and minutes. He observed that the display on one clock changed to the next minute 10 seconds before the correct time, whereas the display on the other clock changed to the next minute 10 seconds after the correct time. For what fraction of the day did the clocks show the same time?

Only one letter is not on the Periodic Table, Which letter is it? _____________