Definition of post-stimulus

[zweckanschauer]

Hi all, may I ask whether the standard definition (if one exists) of post-stimulus means:

1. After the onset of the stimulus, or
2. After the stimulus disappears?

In context, does 24ms post-stimulus of a stimulus lasting for 1000ms mean:

1. 24ms after the stimulus starts to be presented, or
2. 24ms after the stimulus disappears?

Thanks.