Glitter, I reread your introduction. When he starts dialysis, you will be assigned a SSW. You'll have to sign a bunch of papers and given a bunch of information to read. Including a booklet on Medicare and Kidney Patients.
So, to answer your question, if you are going to do "home" dialysis, then Medicare starts immediately. If you are in "clinic" then you have a 3 month waiting period. Your insurance is primary and Medicare is secondary for 30 months, and then if flip-flops.
The definition of Medicare is: A National Health Plan for those over 65 and those with kidney failure. (abbreviated version)