the tomorrow event's end time is correct, as it is a open_end (line 589 in this patchset) event. plone.app.event handles open_end events as events, which do not have a end date/time explicitly set - the data_postprocessing step does it and sets it to the same day at the end of the day (23:59:59) (see : https://github.com/plone/plone.app.event/blob/plone5/plone/app/event/dx/behaviors.py#L470 ff).