SPAN
Unless you're making a RAW request, your query will return interpolated data, giving you the average values across windows of time.
Using SPAN, you can control the size of the time window.
Time is measured in seconds, so SPAN 120 will ensure that there is 120 seconds (2 minutes) between each sample in your results.
Note that there is no guarantee that your results will actually comply with this timing - in some cases (particularly when dealing with discrete channels or simple drivers), point timing may differ.