Release Response

I am trying to set up a program where:

- the stimulus is presented for a brief period of time, while the user has a key pressed

- the user, depending on the stimulus, will either release the key or continue to hold the key down

- if the user releases the key, I would like the amount of time it took to be recorded; alternatively, if the key is not released, I would like it to continue to the next stimulus presentation within 2 seconds
- also, even if the user did make a "release response", I would like the next stimuli to be presented 2 seconds after the presentation of the stimuli that was just responded to.

In case I am not clear, I will provide an example:

a square that is either blue or green will appear in front of a user who is perpetually holding a key down. They should have no more than 2 seconds to make a response, and if they see a blue square they should release the key they were holding, and should be able to press it back down again immediately in preparation for the next presentation of a square.

If anyone can help me with this, I would greatly appreciate it.