Haven't tried this yet....do you mean the already existing entries in Calendar are deleted ?

The options available in Preferences are nice, but are not saved on closing the app !

And the more I try the app out, the more I think the clock face really should be bigger.
Partly because setting up time slots on it is not that immediately intuitive for users who are used to the 'ordinary' way of reading off a clock face.

*edit*
Currently the fastest, most efficient way to use this app is to render a pie slice, then toggle quickly to scribble mode and to jot the event name next to the slice.
Is it planned to be able to save multiple days like this ? I imagine a toggle or button in Todoy that quickly opens the default Calendar month overview and allows one to select a day. Tapping on that day will pull up the graphic pie from Todoy for viewing or editing.