In the US you need to preregister.  But it can be as late as 15-30
minutes before the test. The test is downloaded into the testing
centers computer.  So it just depends on available testing booths.
Note you can schedule a test on the weekend, if scheduled Monday thru
Friday, they can't schedule new downloads on Saturday or Sunday.
 
The Big Red Exam, and the Clark tests allow you limited use, or limited
question pool, until registered 
 
Mike Bader, CNE
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