Sounds like fun, but I think you might have some issues with that.
-security spiders can also have admin rights (not all do, but some will). So if they go in their own system, they will trigger an alert as well
-I assume your time period is at night. A lot of big software updates (and hardware as well, but that's not in scope here) are done during nights and week-ends, to avoid the need to stop working. Those updates will most of the time need to be done by people with admin rights and will trigger your alert.
-what is night in one timezone is day in another. So if your company is a multinational, you can have admin access during the night because those admins are in another country where it's regular day time.
You can trigger alerts, but if any of the above conditions apply too much, security spiders will not take alerts serious anymore.
What you can do is to trigger an alert if the person accessing the system is not at a certain location, or if the request is coming from any other than a certain sub-set of machines. Hardware keys are also very useful in this regard, as the team first will need to have one of those.
What might be fun is to have the system be down for maintenance. If your hacker (or other people who might get to the information, like the face asking stuff from a secretary) didn't do their legwork correctly, they don't know. They won't be able to access the system because the server has been taken offline to replace a component. Please come back in three hours and it should be up and running again.
