I am trying to use a calculated date/time variable to update a start and end time of a calendar item through workflow.  I've logged the output of the calculated date and time (from the add time to date action) and it seems to follow the standard SharePoint Date Model:

8/5/2015 8:00:00 AM

This format does not update the calendar item start time however, whose format I assume is:

8/5/2015 8:00

I've used a replace string action to remove the trailing ":00 AM" but that also does not seem to work.

Is anyone familiar with the correct format for updating start/end times on Calendar Items for Exchange Online?