Sort by multiple (optional) meta keys.

Hello all,

I am wondering if the following is possible:

I have a custom post type called Calendar. In this CPT it’s possible to create events. Sorting by just the date (which is mandatory) is working, however, I also want to be able to sort on a time if the dates are the same.

So for instance, I have 3 events on december 27th. First is at 9:00 am, second at 1:00pm and the third is at 3:00 pm, I want to get a list in that order. So date is mandatory, but time is optional.

I am guessing I need to do something with the post_orderby filter, but I am not sure what. So any tips or kicks in the right direction would be greatly appreciated ??

Thanks.

Mark