Doesn’t Heisenberg’s uncertainty principle mean that we can only read such a clock by upsetting its perfect timing? It might be a perpetual clock, but it would be so fragile that the first person to look at it would cause it to shatter. Besides a clock requires two components: an oscillator to emit time ticks and an accumulator to count them. This is half a clock at best, an oscillator. Without an accumulator to count the ticks, its worthless. The first tick you count is the last one it emits.
You are exactly right.