Method to post challenges/game times for other players to see.
So if I was likely to hop on between 7-9 on Sunday, I could have a little note in the lobby when I'm not there stating when I'd likely be on.
That way, if nobody is on, you still have a tentative idea of when someone is likely to hop on.
Until we can implement an in-game challenge feature, why not use the Events forum to post challenges or game meetups to other players?
Baker has also posted a poll for when players are likely to be online that you can vote in at: https://heromages.com/forums/index.php?topic=16.0 We will be using the results of this poll to help us in scheduling D20Studios sponsored game sessions as well.
I'd say just to get things kicking, have a "virtual gamenight." On fridays me and my friends play lan / xbox games at a certain time, usually 8pm-2am, and we meet rain or shine, even easier to do online. Why not have certain weekday/weekends posted to the main page to alert players that there is sure to be a lot of people on playing a certain time, and then of course we could also play whenever else we wanted ;)