help with cues and ISIs

i’m trying to program an experiment. basically the setup is as follows: 1) a scene shown for 500ms, 2) an ISI for 500 ms 3) another scene.
during the ISI a cue could appear at either 0, 50, 100, or 400ms into the 500ms ISI.
my problem is that i have created a stimulus with the cue. but im not sure how to have it appear randomly at each of these times during the 500ms ISI.
can anyone help?

During the ISI should the cue appear at the same time as the ISI? When exactly do you want the cue to start within the ISI?