EMC Avamar/ DD 880 Decommissioning Task & Time

Customer has a legacy backup and is moving to a new backup environment.

Customer primarily wants to decommission  Data Domain 880 in the legacy environment, which consists of legacy data. Once legacy data is drained and backup up to a new target backup infrastructure, My question is:

How much time would it take to decommission DD 880, considering:

Total legacy data volume residing in Data Domain with Networker is 55 TB Post Compressed (~632 TB Pre-Compressed).

Also,

If the tasks required for doing the same would be also highlighted it would be of great help…

Cheers!

Maddy