You may have your workflow to sync pwdHash to run every few minutes, but you’ve noticed that the completion time varies from a few minutes to several hours.
By design. Normally a workflow to sync pwdHash for a large user base (i.e. 11000 users) should run for a couple of hours. But since the workflow is configured to run every few minutes, QC will report completion incorrectly while the workflows continue to run in the background. QC will not report if you have 2 or more workflows running simultaneously
Run the workflow without any schedules and measure how much time it takes to complete.
Based on this info schedule then your workflow, this will ensure scheduled workflows do not start before the previous run is completed.