I'm the opposite. I'm much less anxious during the day. If I get up and go out in the morning, I find it so much easier to be out and to talk to people and be social.
I don't know what it is in the evening, but I'm less comfortable going out, and I get waaay more anxiety.
I guess it's a similar thing, in the morning I've just woken up so I'm still a bit tired...