Resource availability in resource information only influences the overtime calculation
If you tried to set the resources availability in the resource information dialog (see the picture) you might have thought that it will influence the task duration, but it doesn't.
One might think that if you set the resource availability to 0% it will automatically prolong the resources tasks (depending on the task type) but it will not. The task will have the same date of start and the same end date. The only thing that will change, is the over allocation, that will be reported with an appropriate report.
When you want to make the resource unavailable, you have to click on the Change working hour button, and set an exception.
L.