Create a backup with a different "timestamp"

I used a different backup solution before switching to Duplicacy. I like to mount my old backups and create just create backups from them to Duplicacy to avoid having to store two different backup types for a long time.

But I couldn’t find a way to specify the “timestamp” of the backup when running Duplicacy on the console. How do I do this?

I tried faketime, but this doesn’t work for duplicacy (I don’t know why):

$ duplicacy list --id i3
Storage set to sftp://123@456/backups/duplicacy
Snapshot i3 revision 1 created at 2022-04-28 14:20 -hash

While I started this backup with faketime:

faketime -m -f "@2020-04-30 19:32:22" duplicacy backup -stats -threads 4