Date queries (feature suggestion)

I'd like to suggest date/time queries as a feature. Example syntax would be something like:

@date (hour<12){ /*morning style*/ }
@date (month==12 & day==25){ /*Christmas style*/ }

It's possible to do something similar with server-side languages, of course, but that approach has several problems: it causes issues with cacheing, it uses the server's timezone instead of the viewer's, it increases load on the server, and it is only available if there *is* a server.