But you typically run off firm promises of cash from investors. Then you only need a couple of weeks cash in the bank, and the investors promise to make cash available on demand as you need it.
In my experience with small SV companies over the last several decades, this would be exceptional. Typically you get money from investors at negotiated, spaced points in time. In between your CFO manages the cash on hand to cover everything: payroll, taxes, and any other accounts payable.
This is a leveraged operating model. It’s risky and tanked many firms when the CP markets froze in ‘08.