Click on the Venue's name
On the left side, scroll down to 'Close Areas'
First select if you want to close areas individual by Table/Area or by Zone
Then select when you want to close these areas, either for a particular Date or if you wish to close the area(s) on a recurring weekday
Finally, select the time range you want to close the areas. If you extend this past midnight, Collins will still treat this as the same day and close/shade the areas in the diary in the same way.
Once you do this, you'll see that the tables in the Diary/Floorplan view are shaded off, to indicate that these have been closed.