your question is incomplete

It is impossible to check a complete application within an 
hour.

But if whenever thee situation occurs then 
you should adapt suitable testing method like
adhovc testing.

Adhoc testing won't have any testcases and testplan tester
will conduct the test with his own sense to find and major 
functionality defects.

This is nothing but checking main all modules and defect 
prone areas.
Main intention is to find major defects in the application.
But this cannot reveal all the defects in the application.
if you still  have any doubt feel free to mail me:  
rajendra_penumalli@yahoo.com
or call me:9885162742

Rajendra 
The application is new to tester and for adhoc testing a 
tester has to be aware of application.In this case tester 
can perform Monkey testing.

Narmata

You are 100% correct in this. for doing Ad-hoc testig a 
tester need to have complete idea on the application which 
he is going to test.

In this case a tester can only do a monkey/gorilla testing.