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Where to put a random duration fixation cross

I would like my fixation cross to be presented for a random duration (between 2-4 seconds) before the stimulus is presented.
My question is whether it is ok to place the fixation cross in its own trial before the trial containing the stimulus, or whether they should be in the same trial and have the stimulus onset time calculated based on the randomly chosen duration of the fixation cross?

That is certainly the easiest way to do it. (Note that conceptually, the two routines are just parts of the same trial.)