Realistically speaking, the timing of any of Kyndryl's actions will be customer-driven rather than by the terms of the IBM/Kyndryl split. Given the nature of typical outsourcing agreements, not a single thing will be "moved", "migrated" or even "rebooted" without customer approval. In the outsourcing business, "IBM/Kyndryl policy and procedure" means "customer policy and procedure". They are one and the same, and they are dictated in the terms of service in the contract.
What this means to outside observers: Kyndryl won't do anything different from the past until customer contracts expire. As contracts are revisited, changes will be made if so desired. Stuff can be migrated to new locations and new platforms, or they can be left in place for the sake of stability. It's up to the customers, not Kyndryl and not IBM.