Instance configurations for timberfs@.service live in this directory.
Each <instance>.conf defines the environment for one timberfs mount:
BACKING=/var/log/timberfs-backing/applogs
MOUNTPOINT=/var/log/apps
EXTRA_OPTS=--allow-other
Then: systemctl enable --now timberfs@<instance>
A commented example: /usr/share/doc/timberfs/examples/timberfs.conf.example
Manual: man 1 timberfs