The M103 and M104 engines don't need the timing chain to be replaced, probably ever.
The chains are very short, unlike the chains on the V8's which are very long. The six-cylinders also have a racheting tensioner which keeps the chain tight.
You'll probably never need to touch it.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".