What is your personal marker for knowing when it's time to pop the question?

It depends on how old you are. If you are younger, you can afford to waste time hesitating... If you are older and have some life experience, you will surely know what you want. When it comes to pop the question, there is always sort of awkwardness and you can never be sure when is the right time. Any time could be the right time. So, if you are sure in what you want, stop thinking. Just do it.