Separate date and time in #powerpivot (and #bism tabular)

In PowerPivot you can import data from several sources and it is often the case that you import a DateTime column from a database. From an analytical point of view, you usually make analysis over dates (day/month/year/quarter/week) and over time (hour/minute) but to do that it is often useful to have two independent set of attributes: one for the date (the Calendar table) and one for time (for those businesses where this element is relevant). When your table is not too big, you might import the table with the original DateTime column and only then you can create derived calculated columns in DAX. However, when your table is big (i.e. millions of rows, or more), then it is a good idea to make the calculation outside PowerPivot.