Circles and skill levels matter much, much less in Plat. Making some wild guesses I'd say that we have a group of regular players that probably average in the 60-80 circle range. But then, I've been playing regularly for the past five years and don't have a character over circle 35. And I can say that it's never mattered at all. I've been on quests with characters less than circle 10. I'd venture another guess and say that at any given time the population is over represented in the high and low ranges and under represented in the mid ranges. Plat is a very 'stuff' rich environment. It's pretty easy to get unique items quickly, so that takes some of the sting out of being a beginner again.
As for off-hours, the vast majority of events happen in the 8pm to 10pm EST range. If you're playing from the UK you will probably find us population-challanged as well. Don't know about the LTB's.
Sibley's player