Hey friend.. I think anything from afternoon to late night european time, or mid day to night in the US, there will be loads of people. The only time I really dont see anybody is morning to before-midday in european time when most US people are sleeping and europeans are working or busy in the morning.
Another thing to note is that sometimes the welcome area chat seems empty, but people are hanging out in the chatroom for full members.. But if you write something in the welcome area chat and wait a bit, the full members will come hang out there and talk to you.
Be well