Well, I tried running dedupe on a single folder that has Total usage: 706.166Gi, Objects: 4.189k
and it canceled it after 6 hours (returning 1 set of dupes)
And I didn't see any indication of how much was left.
dedupe considers files to be identical if they have the same file path and the same hash. If the backend does not support hashes (e.g. crypt wrapping Google Drive) then they will never be found to be identical. If you use the --size-only flag then files will be considered identical if they have the same size (any hash will be ignored). This can be useful on crypt backends which do not support hashes.
Are you using the --size-only? This isn't a reccommendation, but based on the documentation you'll need to deal with the caveats of this flag.