When your Calendar view is set to “Month” and you double click on a specific day to schedule a new appointment on that day, the default is an “All day event” since you clicked on an entire day.
To work around this, first select the day that you want to create the appointment on and then click on the “New Appointment” or “New Meeting” button.
This way, the “All Day Event” option won't be selected and instead the starting time will match the start time of your configured “Work hours”, the duration is set to 30 minutes and of course the currently selected date is filled out automatically as well.