This paragraph reads like a response to the criticism they received a few days ago for scheduling maintenance at 2pm PST:
On June 23rd we performed a credential roll on these Redis servers in our US cloud during a two hour scheduled maintenance window. Because we operate a service used globally, there is a less-than 10% difference in usage between so-called "peak hours" and “non-peak” hours. We scheduled maintenance for this time because it was not a peak time, but moreso because this period has high coverage from relevant engineering teams, should issues arise. By performing maintenance during this period, we were able to react more quickly and muster those teams within seconds.
So, doing maintenance on US servers, on a Friday, during a timeframe when the US is getting off work is not a peak period of time for those servers? That sounds a bit like using numbers to lie, or at least minimalize the impact.
I can see how it might have been a lull when considering all Heroku instances (since most of Europe is headed off to bed), but I have the feeling this was not the case for the US servers. I could certainly be wrong, since I'm just speculating, but it just seems fishy.
Heroku only has two regions, Europe and US. Many applications not targetting the American market are still hosted on the US region. For instance, I live in Japan, and all the heroku applications I know of are hosted in the US region. Additionally, as I understand it, most of Heroku's resources are used by a small number of large, international services, who's usage times don't necessarily correspond to USA hours.
On June 23rd we performed a credential roll on these Redis servers in our US cloud during a two hour scheduled maintenance window. Because we operate a service used globally, there is a less-than 10% difference in usage between so-called "peak hours" and “non-peak” hours. We scheduled maintenance for this time because it was not a peak time, but moreso because this period has high coverage from relevant engineering teams, should issues arise. By performing maintenance during this period, we were able to react more quickly and muster those teams within seconds.