Anything over five minutes will cause the engine to explode.

Or, in some cases, like in Bonanzas, Barons, and R182's, the prop can
suddenly depart the aircraft. It is a well established problem from running
at max power for extended periods of time. The actual time it takes for this
to occur depends on a number of conditions, such as ambient temperature,
CHT, age and hours on the engine and oil, etc.