From product launch. The point is to launch something that you can imagine selling $10k/month; that you have some kind of plan how to get to that level of sales; and that you'll hold yourself accountable after three months if it fails (and figure out what to do next, not just stick to the thing that wasn't working).
$10k MMR sounds like a lot of money, but it is not. Most people who have never run a business fail to realize how much overhead there is - costs that the business has to pay that isn't labor or obvious materials. If you make a widget from iron it is easy to calculate the cost of the iron in the widget. Did you ever consider how much toilet bowl cleaner is in each widget though, what about your time to clean the toilet? (once you are making more money you pay someone else to clean the toilet, but you still have to account for your time checking that they actually clean it) $10k MMR sounds like a lot, but after overhead I would expect it would give you the equivalent of $50k/year in salary - I think most people reading this make more than that.
To answer your question: The day all your other investment dries up in the worst case. If you have no job or savings you can probably live 3 months on things like your credit cards and not paying the landlord - after those 3 months you better have enough income to start paying your personal debt. That is you need to send the landlord a check for at least 1.5 months rent and with a promise to pay the rest off soon. Likewise you need to be able to buy your groceries with cash and pay down the credit card dept you ran up. It should go without saying that in those 3 months your personal bills should be just enough to stay alive.
Note that the above is the worse case. If you are in month two of the above situation and realize that you won't make the $10kMMR number you should cut your losses, declare bankruptcy and find a day job.
You probably have some savings to live off of though. This means that you have some flexibility. If you are in month 2 and realize you won't make the 10kMMM you can decide if you cut your losses now or not. You have an idea of what your overhead is, who your real competition is and what your leads are (and thus likely future MMR - though don't get over optimistic), if you think things will get better continue, if not cut your losses: you can probably sell to a competitor for a small price and make everyone happy.
If you have investors who are any good at all they have considered your business plan. Sometimes they will insist on the 10kMMR or they will exit, other times they will agree to fund a plan that won't make money for months - but the plan covers that and you have enough income from the investors to live.
There are always other considerations to. 10kMMR is a good number, but you have to figure out how it applies. If your target market is snow plows you should expect your entire income to come during the 3 winter months, and 0 the rest of the year. Thus in winter your MMR needs to be at least 40kMMR, and you need a savings plan of some sort to get through summer.
Don't forget that you can sometimes moonlight. Maybe your ideal is only worth $2kMMR. If you can support this business working only 8 hours a month you keep (or find) a day job for most of your income. That extra 8 hours a month works out to $100/hour after overhead. This again changes the calculations.
