Someone on broadcast radio said this is the first darkness landing. I don't know if it is or not.
I am still wondering why they are landing at this time. I also heard there was atleast one later opportunity (9:18am) and possibly a third window.
That report is incorrect. There have been numerous night landings of the Space Shuttle. Several Shuttle Commanders actually prefer night landings at KSC because the runway is brilliantly lit at KSC and presents a clear target without the other visible distractions during daylight. Rain storms are also less likely to crop up in the early morning hours at KSC. All things considered, it's a good time to land from NASA's perspective.
If Discovery lands on its first opportunity, at 4:37 a.m. EDT, it will be the 15th night landing at the Kennedy Space Center.