How to parameterize timecycle expression in timer start event?

We need to specify the cron expression for "Time Cycle" in the start timer event.  We want this as a configurable property on workflow overview page. Tried creating a variable and putting the cron expression in the form properties of the timer start event and used that variable as ${<var name>} in Time cycle, however it is throwing error while deploying the WF stating the "Cannot resolve identifier".

Any idea please on how to parameterize this? When migrated using the migration export-import feature to higher env, we are not able to modify xml and can not change the cron exp.