I've noticed from my data set that when looking back at old data from mid-2000's, a few stocks often won't have any trade volume for early minutes, and then 4-5 minutes into the trading day have their initial spike (~25,000). Example below:
Time: volume
9:30: 0
9:31: 0
9:32: 0
9:33: 0
9:34: 25,000
9:35: 6,000
...
Is this because my data source was delayed in it's collection of data? Or is there something else that can explain this? I know sometimes a stock's opening will be delayed and not occur immediately at 9:30, but patterns like the above are occurring on about 50% of days for some stocks back in the mid-2000s. I hardly see it occur past 2010. Has my source's data acquisition improved with time, or can this be explained another way?
Time: volume
9:30: 0
9:31: 0
9:32: 0
9:33: 0
9:34: 25,000
9:35: 6,000
...
Is this because my data source was delayed in it's collection of data? Or is there something else that can explain this? I know sometimes a stock's opening will be delayed and not occur immediately at 9:30, but patterns like the above are occurring on about 50% of days for some stocks back in the mid-2000s. I hardly see it occur past 2010. Has my source's data acquisition improved with time, or can this be explained another way?