Be careful with Thread Titles in the future. I almost didn't bother reading.

How much time before the appeal needs to be filed?

You need to hire another attorney ASAP or write the appeal yourself.

I received a Partially Favorable Decision (so, my attorney collecting a max fee) for a closed period several years ago. I received backpay, but not ongoing monthly benefits.

My attorney's office kept brushing me off and then with 5 days days left before the appeal was due, notified me that he would not be willing to represent me in the appeal.

I filed the appeal myself by addressing the reasons listed in the Judge's decision. I didn't have time to request the CD from the hearing. My appeal was physically lost by my local office, and I later won a Fully Favorable decision going back to the original injury date at an ALJ hearing where my second application and the misplaced appeal were addressed.

If you do it yourself, walk it in to your local office, and get a copy stamped with the date they accepted receipt.