I'm not sure I understand what exactly are you trying to ask. Could you please elaborated your situation?
Which testing points should covers during testing in short time periods??
In real world, there are many situations in which a tester has condition of limited time. So, which functionality of app should test in this time period??
If time is really limited, then its time for a conversation with your stake holders. Identify what parts of the application are critical to be tested before shipping, and do not except, 'it's all critical'. Make it clear that you want to test effectively, and because of the time crunch you will have to prioritize which areas get the testing focus. Since they are not giving you control of schedule, you can only help them manage risk by focusing on the parts that would most threaten the value of the product.
This is important even if you do feel you have adequate time, because it is rarely ever possible to truly completely test any software purely because of combinatoric concerns.