I believe the third, namely both, in the sense that there are aspects of a causal interaction that are successive as well as aspects that must be simultaneous.

Here is the explanation:

Only simultaneous:

Pro:

The causal links share the same present. Therefore, they can interact with each other.

Contra:

How is one to know which of the causal elements is cause and which effect?

The causation is instantaneous, which is implausible if the effect is not to be an absolute point. Because an effect will always be complex, so that it must unfold temporally first. A causal process takes time to elapse.

Only temporally sequential or successive:

Pro:

One can clearly determine what is cause and what is effect.

The fact that the effect cannot be there with a snap of the fingers is taken into account.

Contra:

How should the cause be able to be in a causal interaction with something future? The effect would be something from the future and there would be actually no contact with the cause.

Ergo:

So both must be in play, each in a different respect.