Sunday night in that timeframe in 2011 was actually not crowded (IMO)...I imagine a lot of people had to be back to work or school on Monday. I was able to get a Space Mountain FP at 9:50 PM (park closed at midnight). I interpret that as meaning crowds overall on Sunday weren't that bad...most times when I go, Space Mountain FPs are gone by the afternoon.
2012 could be different because of Cars Land bringing in bigger crowds, but I'd still think Sunday night may not be so bad.