Agent availability is a short term figure. It defines the percentage of time during the period under analysis that an agent is available for handling calls. For example, if during an hour, they perform 12 minutes of administrative work and, during that time, are not available to handle calls, then the Agent Availability is 80%. However, Agent Availability is not the same a wrap up time. Wrap up time is the time after each call that an agent is not available. The time used to calculate Agent Availability is not call dependant.
The point is, it is not a long term figure and does not take illness, holiday etc. into account.
I hope that helps.