Conrad plays with readers’ sense of time to emphasize certain points in the plot. Marlow tells his story aboard the Nellie so readers go with him (as well as his listeners) into the past. Simultaneously, we readers in real time watch the reactions of Marlow’s listeners as they respond to Marlow’s story. Marlow’s journey into the interior is also described as a journey back in time, to a prehistoric age during which the untouched wilderness proves primal and merciless. The river itself comes to represent the linear flow of time, on which Marlow travels forwards and backwards.
Conrad uses well-placed delays in Marlow’s journey, long descriptive passages, and incompetent members of the Company to prolong time and induce a suspenseful atmosphere.
The river is a symbol of linear time that Marlow and his crew traverse; as they go further and further up the river, they feel as if they are receding further back in time.