CAT aspirants: are you preparing for WAT-PI already, or only after results?

CAT is done for a lot of us and the usual advice is "start WAT-PI prep now, don't wait for the result". I get the logic, but I'm finding it hard to take it seriously before I even know which calls I'll get.

What I'm thinking of doing for now:

• One timed WAT essay every two days, on a mix of business and abstract topics.
• Writing proper answers to "tell me about yourself", "why MBA" and "why now", and saying them out loud rather than just writing them.
• Revising my graduation subject, because apparently panels love asking engineers about second-year topics.

For people who've been through the process: how early did you start? Was it worth practising the PI out loud with someone asking follow-up questions, or is writing the answers enough at this stage? And how did you stop your "why MBA" answer sounding memorised?