This probably sounds strange, but for me it would be as from the moment the sandwiches aren't free anymore.
Let me clarify: I don't think it's something measurable, it's when you start noticing small things like, for example, sandwiches aren't free anymore or drinks after work with the whole team are cancelled because the founders have to go to meetings with clients/investors for the 4th time in a row. It's just small things...
While I understand your focus, I don't think you should ignore the culture aspect.
E.g. it's not original to me, but you're be sure it's true when your probably new CFO ends free soda for no other reason than to make himself look good (i.e. not in response to a change in the company's financial situation), and the rest of the board/CxOs doesn't care (much).
When the founders no longer know the names of all their employees.
So, the entire point with starting a company is to make wealth. This wealth is traded with money. The day your company create so much wealth that you go break-even, that will be the day you have established a profitable company, and you can be considered entering the phase of intrepreneurship (meaning to work on a already established business-model). A startup is entrepreneurship. So the next question would be: is this model which I've "entrepreneured" sustainable? Will it continue to grow?
To sum it up, I would say that 'entrepreneurship is act of creating a profitable business - where as intrepreneurship is the act of maintaining it'. I would also add that the distinct difference between those two people, is the willingness to take risk one often see in entrepreneurs. Whereas maybe inrepeneurship is handed to college-kids with an degree.