Hello Harry,
You yourself have mentioned the exact use of "start using meta chain or api". It is used to create a main chain which will have many different chains in sequence.
The start variant gives you an option of executing the chain either by a meta chain(chain inside a chain) or directly.
Suppose you have process chain A an B.
1. GOTO Start variant of A chain and schedule it via start using meta chain or api.
2. Similarly for chain B schedule it by start using meta chain or api.
4. Now create a new process chain Z which will have chain A and B in sequence.
5. Schedule chain Z by Direct scheduling. Under Change selections goto time and select data and time when you want to run this chain.
6. For each chain A, B and Z. goto rspc1--> chain name--> under menu EXECUTION--> Schedule.
Now Chain Z is the metachian which has chain A and B inside it.
Z will start at your desired time. It will run A first and after A finishes it will start B.
You can also run the chains A& B in parallel as per your need.
Hope this gives a brief idea to your question. Assign points if helpful.
Regards,
Amit