The Longman’s dictionary you consulted already explains the countable and uncountable sense of occupancy:
noun [uncountable] formal
 the number of people who stay, work, or live in a room or building at the same time
single occupancy room rates
e.g. Hotels in Tokyo enjoy over 90% occupancy. [uncountable example]
 someone’s use of a building, hotel, or other space, for living or working in, or the period during which they live or work there
e.g. The day for changing from one occupancy to the next was on a Saturday. [countable example]
Sense 2, therefore must be the “countable” sense, although it fails to directly mention this, the example for number 2 shows this, and other dictionaries mentions its countable sense.