This idea is not necessarily true: WoW's population plummets down to almost nothing every morning from about 2:00AM - 10:00AM and, on weekdays, only hits a decent amount of people for a few hours each evening. Additionally, the average number of active characters is, more often than not, under 700 for a given faction.
When I used to play (which was not long ago), I would try and queue for a dungeon / PvP (which queues across all servers) from 7:45AM - 8:45AM every morning, and I never once got in a group.
Here's a source that proves that there are huge "wrong times" to play WoW and yet that seems to in no way affect its success.
A couple things about this post are misleading - and folks really need to have the facts.
1. WoW servers are separated into Latin America, North America, Oceanic, and European (the ones I know of). In fact, Europe has their own client download which won't allow them to see the sets of realms over here and we can't see them without their client. So there is a set of realms to choose from that is appropriate to your time zone, it's not the "melting pot" of XI and XIV where everyone is on the same set of servers no matter where they are.
2. You aren't put in a queue across all servers
, you are put in a queue across the servers in your battlegroup
which is a cluster of servers. It's definitely possible that you didn't get into a group especially if you were say, a DPS which there is a surplus of. You don't specify, but to give a little perspective here during peak hours for a heroic dungeon a DPS could be in the queue for half an hour before getting a group, while tanks and healers are almost instantaneous.
If your playtime was not what is considered the "standard" NA playtime then you could have selected a different set of realms that was closer to the time of day that you play.
Now, I'm not taking sides on which method is the "better" method, just offering some insight and corrections as this post is incredibly misleading about the facts in WoW.