Edited from misreading the chart.
That chart is way out of date, especially since the move to cloud servers.
And, I always thought that the East Coast servers were at 5 AM Eastern, not 6. There was a statement about a decade ago, that they tried to get server maintenance around 5 AM local time when possible.
At least the chart is up to date in regards to the US Central server farm not being listed, which hasn't existed since 2001. That's when they moved the Central Servers to the same servers as Atlantic, etc. outside DC. Some charts I've seen still referred to it (and before I realized the top line was time zones, I thought this was one of them).
Strangely, even 2-3 years after (and some people to this day) insist the server is not only still around, but that Lake Austin is on it (when Lake Austin, from the moment it went live, was in the west coast server farm, and at best might have been on a server in Austin for a couple weeks before going live, undergoing internal testing, before being shipped out to California to be installed). I know that the people who brought me into UO in 2003 (in Kentucky) thought it centrally-located, hence why they left GL & LS to start fresh on LA (and swore up and down they were getting twice-better pings to LA than to the east-coast shards).