Yesterday was the first time it occurred on my car so was hoping for the best, but always had it in mid to have it swapped at the first sign of trouble.
I understand that its the oil draining out of the tensioner that allows the poorly designed ratchet mechanism inside to compress, thereby allowing the cam chain to lose tension. As there is slack in the chain, the cam timing moves, allowing valves to hit pistons.
In normal service, the tensioner is kept tight by the engine oil pressure. Thats why the early symptoms disapear as the oil pressure produced when the engine starts pumps up the tensioner. Thats why I changed to a slightly thicker oil, to try and help the tensioner retain oil overnight.