What time of the day is worst for spam complaints?

Following on from my other post for which day of the week is worst for spam, I decided to look into what hours of the day are worst for spam?

Now, keep in mind that this is not our inbound spam, it is our outbound spam.  I monitor the size of the number of spam reports and use that as a guide for when spam outbreaks are likely to occur.

In the chart below, the complaints axis isn't actually raw number of complaints, the results are normalized.  But we can see that about 8 am Pacific is when the spam problems really start to escalate.  This would be about 11 am on the east coast of the United States.

Why this time period?  I really don't know.  Educational institutions compromise over 80% of our outbound spam.  What's special about 11 am?  If it were 8 am, I could see it since that's when a lot of people get in, but the bottom line is that there is a period of about 8 hours corresponding to a day's work when most of the spam is occurring.

Combining these two data points together, the worst time for outbound spam problems are 8 am on Saturdays... the time when I am (personally) very unlikely to be paying attention.