SQL Server 2012 Data Loss Time Defining Using Availability Group

Greeting Everyone,

Hope you guys are good and everything would be good. 

I am new to SQL server 2012 AG. I have a setup of four node Multisite Failover Clustering of SQL Server 2012 using Availaibilty Group. I tested out Windows Level Failover Clustering and also temporary create database in SQL Server 2012 and test Failover. It's works fine :).

My question is that in case of a Disaster where we should define timelines of Data loss or if we do not define data loss time then how much data should we loss?

Also if someone share a very small application for which testing of this scenario, which will read and write in SQL Database at real time.

Thanks & Regards,

Mohsin