Answer:
1 second.
Explanation:
Sensory registers refer to the most immediate form of memory people have. It's the first one, the quicker one.
This memory is in shor term, which means memories won't last long here.
Basically, sensory registers just take information from your sense, and then it keeps it for not more than a few seconds.
Imagine that this memory last longer that it should, that would mean you cannot forget all informations your sense perceived in the last 30 minutes, that would be hell, actually.
Therefore, the best answer is "1 second".