Will APNs become invalid immediately after the app transfer is completed?

Hello, I have a question regarding push services after app transfer completion and hope you can clarify it for me:

1. If the original team does not actively disable existing APNs and JWT connections as well as push services, will the old P12 certificates and P8 keys remain valid for a short while so users can still receive push notifications? If yes, the new company only needs to finish certificate updates shortly after receiving the transfer success notice. How many hours is this grace period normally?
2. Whether the original team shuts down APNs and JWT services or not, will the old P12 certificates and P8 keys become invalid right away, leaving users unable to receive pushes until the new company updates the relevant credentials?

Thanks for your support and looking forward to your reply.