I think I'd rather change it from a property to a method at the same time - 
"Midnight" isn't logically a property of a date. The same argument pretty much 
holds for LocalDateTime as a property name, which is another reason to change 
it.

I think if you want to represent "midnight on a date" and "noon on a date" then 
it would be more sensible to have a Noon constant on LocalTime, so you could 
use:

    var noon = date + LocalTime.Noon;
    var midnight = date + LocalTime.Midnight;

(The addition operator is already present, unless my memory's going.)

Will consider what the method should be called...

Yes, I quickly stopped using .LocalDateTime and use "date + LocalTime.Midnight" 
instead because the intent is clearer and I'm calculating lots of other 
relevant time ranges like afternoon, evening, night, ... so the pattern is the 
same if I use "+ LocalTime".

Right. I think date.AtMidnight() is probably reasonable as a method, as it has 
better discoverability than the + operator (which I'm not planning on removing, 
of course).

Will make the change when I get a chance, which may or may not be tonight...

Fixed in revision ff469eb394c2.