This call registers and onboards the Polkadot Coretime Chain based on the v1.3.0 release. Instructions to reproduce the chain-spec and genesis data are included in the release. A chain-spec is included there for node operators, and will also be added to the polkadot-sdk repository with the other system chain-specs.
This does not initiate the migration to Agile Coretime, but is a prerequisite before the migration can be run. A follow-up referendum will update the Polkadot Relay Chain and migrate existing leases to the Coretime Chain, then a third referendum will configure the Coretime Chain and start the sales.