The simplest, but not the only way, would be to setup the 'polling' operator(s) inside a Loop Operator with a Delay operator as the final (or first) activity. You can run this 24/7 - though remember PAM has to store ALL running processes in Memory, and will grow in size the longer it is run, so if your process is very large, you run many of them at once, or you have been looping for a long time, you may start to run into memory usage issues.
Another way would be to build a simple process that does the polling activity, does whatever is necessary such as start a another process under certain conditions, and then complete. You would then setup a Schedule to run when you need to do the polling. This has the benefit of not leaving the process in memory.
Michael Niebuhr