How to change startEvent.timeDuration at run time?


I am new to Flowable. Currently using 6.6.0. My requirement is that the first task is the userinput task where I will take the timeDuration as input from user and then later i want to change this timeduration of startEvent and the timeduration which will be in days must be set accordingly after the userinput task and later the flow should get triggered as per this duration.

If user wants to change the timeDuration he can again do the same by entering a different value from front end in the user task and then the timeDuration should get modified.

I can keep a default value for timeDuration at startevent but it should get changed as per the input from user. Can i handle this in bpmn? If yes, then can you give an example?

Thanks for the help