A custom control, like the calendar component shown here, requires many subviews. In fact, to generate this view requires about 700 subviews, unless manually user-drawn.
Apple's AutoLayout was introduced in iOS6 to provide a means to layout user interfaces independently of screen size, aspect-ration, and resolution. Unfortunately it is very ineffecient and appears to have an order of O(c^n) i.e. every subview added makes the layout take exponentially longer.
The control that is shown, designed to use AutoLayout, takes up to 10 seconds to render on an iPad. This essentially makes it unusable.
In examining the execution using Instruments I came to the realization that it was all Apple code that was swallowing all this time. Eventually I found two others who came to the same conclusion the hard way:
By turning off AutoLayout, the calendar renders (incorrectly of course) in a fraction of a second. I'll be spending this weekend writing my own MagicLayout code, which will be used by the cross-platform component library that is in development.