Assuming that the asset underlying a futures contract pays no dividends or associated (storage, etc) costs, I have the following formula for the price F_t of a futures contract at time t:

F_t = S_t * e^{r (T-t)}

where S_t is the value of the underlying asset at time t, r is the risk-free rate, and T is the contracts delivery date.

Suppose that F_t < 0. If I were to take a long position on this contract at time t in a real world situation, would I immediately receive the amount F_t, or would all money change hands only at delivery time T?

F_t = S_t * e^{r (T-t)}

where S_t is the value of the underlying asset at time t, r is the risk-free rate, and T is the contracts delivery date.

Suppose that F_t < 0. If I were to take a long position on this contract at time t in a real world situation, would I immediately receive the amount F_t, or would all money change hands only at delivery time T?