Dynamic cyclic timer initalization where timer variable is fetched from existing service in execution listener

As part of a main process, I have set up an event sub process as follows:

image

The timer is configured as follows:

The issue is that ${cycleRepeat} does not seem available (independent of calling a service or not). This is the consequential error:

org.camunda.bpm.engine.ProcessEngineException: Unknown property used in expression: R/PT${cycleRepeat}S. Cause: Cannot resolve identifier 'cycleRepeat'

I assume, it’s a fundamental misunderstanding on how the sequential execution path of a bpmn node during runtime is, however, I would have assumed that the execution listeners would be run before the actual timer setup. But that assumption must not hold.

The question is: how would I achieve my desired setup?