If you are concerned about the length of time an individual process is running, you could set up the process to call itself as detached after a certain number of tries. For example:
Say the definition is called Send-Email-Reminder:
1) Process Instance starts and begins delay for 2 hours
2) Delay ends and email is sent. Process delays again for 2 hours.
3) After x number of emails, process instance will call a detached instance of Send-Email Reminder and terminate
However, If you are using Service Desk Manager for the ticketing, you could use SLA Events for these reminders. This would be more efficient and would not need Process Automation.