how to measure the movement time for two tasks

Hi guys,

I'm currently planning to design an experiment using Matlab programming. In my study, I'm going to have two stimuli presented to the participants (hereafter, S1 and S2). The participants need to press the homekey and waiting for the fixation point. After fixation, the first stimulus (S1) will be presented and the participants need to release the homekey and press the correct response key within 800ms. Later (after about 1000ms), the second stimulus (S2) would be presented to the participants after S1 has been presented and responded. Then, the participants would have to release either the homekey (after responding to S1, they need to press the home key again) or S1 response key and respond to S2.

The time I would like to measure is the time interval between the onset of S1/S2 stimulus and the onset of releasing homekey. Also, I would like to measure the time interval between the onset of releasing homekey and the onset of pressing the response key.

Thanks!