According to this Data archive buckets explained pressure is always the pressure at that exact point in time, except when watching a graph that is completely zoomed out, then it is an average (I assume the average from the 3 hour measurements or from all the 1 minute samples, but that isn’t specified…yet).
For your analysis, if the pressure is sampled every minute, it would be fair to assume that it would be the best representation for the actual pressure during the interval from half a minute before a specific time, to half a minute after that specific time.