The way I look at the overlapping aspect is to think of hypertime as a network of rivers. They all flow in the same direction, but sometimes they diverge and reconnect (such as when there’s an island in the middle of the river). A particular timeline is the path each water molecule takes as it goes from one part of the river to another. Many of these paths will cross each other and overlap, and the molecules themselves will knock into each other, influencing the paths they take.
It’s the idea of the “timestream” taken a step further.