You can have the macro wait until the tmutil command is not running.
Something like this:
-
While the shell command “ps auxw” result contains “tmutil”
- Pause 20 seconds
- Unmount disk
- Notify
For this sort of thing, where it is going to go for a long time, and there is no need for a rapid response at the end, using a While loop with a long pause will cause less CPU/Battery drain than will a Pause Until which will check the continuation at a very high rate, needlessly wasting CPU and battery.