With zero financial investment, I assume that also means no capital assets of any kind. That excludes land, commodities, resources, labor contracts, securities, etc.

I will assume subsistence is available.

With that said, you only have labor and ingenuity. The ingenuity is required to identify something valuable (scarce, in high demand, etc.) from an economic standpoint.

The labor is initially focused on earning enough capital to acquire the necessary tools. Then, that will enable the labor required to make something of value that can be sold for more capital.

The question of time is unanswerable, because it depends on too many factors.