Here is one example: http://freakonomics.com/2012/08/20/this-website-only-open-du... but I'm pretty sure I ran into an issue with the IRS website (how we pay/manage our taxes) but now I can't find mention of it.

Some people have said it may be due to reports that run at night and can't have new data coming in while they run or something similar but I don't buy it. If that's the case then just modify your query such that the data it gets has a "WHERE submitted_date <= <EOD DateTime>".