My challenge was this: 4 x clocks in unexpected locations or unexpectedly embedded in objects
They were all taken in the space of a few hours, not just because I was traveling and paying attention then, but also because there just weren't any other unexpected clocks later in the day.
Victoria Station, Délice de France. I bought a pastry and then noticed the clock. There are not nearly enough shops around with publicly visible clocks. I asked to take a photo of it, and they asked me if I was a tourist.
This clock was so unexpected that I grabbed for my camera with my pastry-greased hand before the train sped up and it went out of sight. In retrospect, I'm sure I've passively noticed it before, but I certainly hadn't remembered it was there.
A man with a clock for a face! I looked up at Bromley South, and there he was. He was less unexpected later in the day, when I regularly encountered him - and his sans serif purple-faced female counterpart - on the platforms of other stations. They're warning of changing schedules; all that inadvertant memorization of train schedules will have been in vain. (The railway's website has other variations on this theme.)
In Canterbury, through the window of an estate agent, I spotted this nifty clock. It's not just a wall clock. It's a pendulum-driven wall clock! That hole at the bottom is a cutaway to show the pendulum oscillating within the clock.