it pulls in an old version of the time crate that flags many
rust projects as being vulnerable to an old CVE.
We still have other references to time that I'll remove in a follow up.
At very high concurrency we can get a bit stuck waiting for
the tasks to finish.
Adjust so that we wait for the desired duration and sample the
count at that point, then we'll proceed to report that without
worrying about joining the sender tasks.