The issue of needing a entry and exit delay for smart home monitor has been brought up since the feature was released and raised directly with the CEO of SmartThings in May, but it hasn’t happened yet.
There are some ways to introduce a delay using custom code, but it’s not very intuitive. You can ask in the core peer assistance thread, I think some people there have done it.
( Core is a very sophisticated community-created rules engine. In core, a single rule is called a “piston.”)