Can I still get a companion certificate in time?

I currently have a Delta Gold AMEX card and my renewal date is in March. I want to use a companion certificate for a planned trip in August. I read that they are eliminating the companion certificate in January for Delta Gold AMEX card members, so I was considering the upgrade to the Delta Platinum AMEX.

If I upgrade now, I assume that I would pay a prorated fee and then the full annual fee would be due upon my renewal date in March. Is this assumption correct?

Also, if the above is true, would I get my Platinum companion certificate shortly after my renewal in March or would I have to wait another year?

Thanks in advance for your help!

Dan