If you still have questions after reading please contact us.
Automatic timers are started and stopped according to the current workflow your project uses. To learn more read When do automatic timers start / stop?
If you want to know more about the way we calculate time please check out How time spent is calculated (with working hours)?
Yes, Clockwork works with Tempo as well, but our plan for the future is to offer similar features that you won't be needing Tempo.
Time spent on the issue is logged only once the timer is stopped. It means that currently Clockwork will log all time spent at the last day. It will not spread the time through days the timer was running.
When working on a sub-task time spent is reported only on the sub-task. Parent issue is not updated so you should not keep the sub-task and the parent issue in progress at the same time.
See Break down time by Organizations from Jira Service Management