30 secs isn't an exact figure but it won't take very long. The main problem with overheating it that everything expands into each other, certain alloys will melt, the water will boil, expanding into steam and warping cylinder heads, as soon as you warp the hear the oil and water come into contact, immulsifying and meaning you suddenly have no lubricunt in your engine causing excess wear and friction, which of course results in more overheating.
It all gets very messy very quickly and usually within about 5 second of initial overheating the engine is cooked, the main problem is its a runaway thing where what starts as a small problem quickly magnifyes where every result has a new effect.
warped head:
broken bore, results of overheating
result, bang:
http://www.lacoctelera.com/myfiles/kare ... tralia.jpg
