Below is a list of clues, in no particular order:
- At 7:00 PM
One order is the correct order. What is this order, and why is it the "correct" order?
Start looking for commonalities in these words. What about them is the same for all words?
Note the "Knowledge" tag and the "English" tag. Take this to mean you might need some uncommon knowledge about the English Language itself. I'm a native speaker and I didn't know about this until recently, so I'd expect not everyone knows about it.
I actually got this idea from a recent Stack Overflow blog post. There's something in there (if you read it long enough) that will help you, though it's not exactly what's going on here. It's very similar, though.