Most attempts will be "nondestructive penetration." If you're willing to damage the case in a highly noticeable manner, a well-padlocked Pelican box can be opened in under three seconds.

Of course, anyone within earshot will be well aware that something has happened...

Since the TSA has been willing to perform "destructive penetration" for lesser reasons, it is logical to assume that a well-padlocked Pelican or other hard case will only serve as a deterrent, and not a prevention.