If you reserve a meeting space from the tablet, a meeting is created that will start straight away.
To enable ad-hoc reservations, open the meeting space/resource record and mark it like so:
Note: when you enable the above items marked in red, please activate the Door Tablet Harvester. See here:
From the tablet you can now look to the bottom of the display and tap "Reserve":
Creating ad-hoc reservations
Door Tablet allows you to create a reservation based on the many rules you have set for the meeting space. For example: