I suppose that this answer is for me because you thought i was questioning your answer,
my answer wasn't an argument to your post,
i gave an answer to the original question and it was actually the same as your answer.
I think the time period of the digital signal should be greater than the sum of hold time, rise time and the tpd (propagation delay) between the input and the output of the FF. (I remember reading this in Timing analysis). Is that what you are asking?