You can't reply to chat or continue a conversation (or interact with the site in any way) while waiting for opponent after creating a challenge. It's a pretty small thing but I just thought I'd mention it.
This will be improved in a couple of weeks as we roll out automatch, it's being tacked in: https://github.com/online-go/online-go.com/issues/179
Why not just open a separate tab with online-go.com?
That seems to work for me. I always do it, even just so I can see what other challenges are open, because the dagnabit "waiting for opponent" dialog obscures them.