I was asked by our client (which owns the contract with Adobe) that they want to:
Please find my answers Inline
You would need to delegate the name server of your sub-domain to campaign.adobe.com once that is done you can raise a support ticket to get the same configured on the instance if hosted by Adobe
2 How long would that new set up take?
Delegating a sub-domain on your end should not take too long usually within a day or two. Once that is done Support should be able to get the rest of the job dine within 3-5 business days.
3 Is there an estimation for the IP warming in time?
It actually depends on the volume you send daily and the data quality. You may refer to the following page for an rough idea
How to Warm Up an IP Address: How Much and When? | SendGrid