Dreaming Mongo

Last night I had a dream. I was wondering about availability of various date formats in MongoDB. The point was that MongoDB native Date type represents both date and time together, while there are lot of applications where time-level precision is not needed. And on a scale MongoDB operates it might be substantial. So the question was if there any native format for date-only. And I hesitated to ask the pros :).
Turned out I actually missed office hours last night - probably the place where it would be appropriate to ask. Looks the dream had some valid cause.