Appointments+ doesn't properly handle 24-hour sessions.

There is an issue with booking a full-day (1440 minutes) session.

Our setup is one provider that has three services:
- Släpkärra (1 timme) - 1h session
- Släpkärra (4 timmar) - 4h session
- Släpkärra (24 timmar) - 24h session

Working times are around the clock (00:00-00:00).

The calendar for 1 and 4 hour services work fine. So if a client books a 4h session then it is properly reflected in the 1h service calendar and vice versa. But the 24h service calendar is broken.

If someone has booked an 1h or 4h session in a day, the 24h session calendar should be instantly unavailable. However this is not the case, the 24h session calendar will still show a free session available (00:00-00:00), and it is possible to double-book.

Here is an example from a test site (4h session calendar):
http://app.khromov.se/skacklinge.se/make-an-appointment/?wcalendar=1380998409&app_service_id=2

We can see that there is a booked time tuesday 04:00-08:00

Then, we look at the 24h session calendar for the same provider:
http://app.khromov.se/skacklinge.se/make-an-appointment/?wcalendar=1380998409&app_service_id=3

The tuesday session appears green and bookable, although we already have a booking that day!

I hope for a fix for this ASAP. It's preventing us from using this plugin since people can double-book services.