I think I run into potential activiti bug.
I've created a simple workflow to reproduce the issue. Please see the attached xml and screenshot. I have a timer that is set to (R4/PT1M) send an email 4 times with one minute interval. Everything works as expected until I introduce (wrap the exiting workflow into) sub-process. With sub-process it correctly waits for 1 min but then instead of sending one email it sends all 4 at once, after what nothing else happens. As if the "R" portion of timeCycle is ignore or firing all at once.
P.S. I'm on activiti version 5.18. And I just found that https://activiti.atlassian.net/browse/ACT-4090 this was solved in 5.21. I will try to upgrade.