Man, you guys worry waaaay to much. It's a timing chain and is designed to last the life of the engine; just the same as the oil pump, bearings, pistons, rings, and all the other internal engine parts. If it had a replacement interval, then BMW would design the engine to easily replace it (e.g. a timing belt).
Yes, it cold fail due to improper assembly, or a manufacturing defect in one of the parts in the system, but it is DESIGNED to last the life of the engine. The design-life of the engine is well past 150,000 miles.