EEM was designed to provide short-running automations. The default max runtime for all policies is 20 seconds. However, this runtime can be extended to huge values. It really depends on the specific use case as to whether it's better to do all the work in one policy, or break things up into multiple policies and chain them together. If the policy will be doing the same thing, but on a large-ish dataset (like interfaces) it would be better to do it all in one policy versus trying to duplicate the logic in multiple policies.
