The VA has a form you can fill out prior to discharge so that once you are discharged you can begin collecting any benefits immediately.
It is form 21-526C, and can be filled out anywhere from 365 days out from separation up to one day out from separation. The difference is which box you click at the top. More than six months out, check the BDD box (benefits delivered at discharge), less than 6 months out check the quick start claim. When you have filled out the form, you need to turn it in with a complete copy of your medical records. The VA will process the claim, assign a tentative rating, and schedule a check up with their own physician to make sure nothing was missed. The form is turned in to the regional VA office for processing, along with the copy of your medical records. Theoretically, you could have your tentative rating from the VA well before your MEB process is completed. AND if for whatever reason you need to claim something else, you just fill out an amendment and submit it. Don't know why they are saying they won't talk to you til you are separated when this is available prior to separation.
They did want an estimate on separation date from those of us undergoing the MEB process, but they did not require the exact date at the TAPS class I went to, and they were accepting forms for turn in during class (assuming people had copies of med records as well...). Downfall in my opinion of waiting until you have separation date is you are potentially going to have only 1-3 months to actually accomplish everything...and there is alot to do besides VA stuff then, including actual outprocessing of military...
Good luck to you in your MEB process, sounds like you deserve a high rating for all your stuff.