You made me laugh with this anecdote!

If it had been me I probably would have said something like he T seems to have said--but not with the thought that I was amazed that you could tell time!--but rather in surprise to learn that there was something wrong with my clock, and that I had not observed it previously. So if I were to say

Oh my gosh, you are right!

It would have been to express surprise and chagrin at the situation itself, not surprise that you were capable of noticing it.