oddly enough when one connects to the Apex administrator workspace, in the instance security settings there is a session inactivity attribute.
Now, this attribute is said to control the inactivity of the internal Apex applications suite, but if you read the contextual help for this setting it says that when you clear the value, the default value is applied and it is 1 hour.
So I am wondering if the apex documentation could be wrong in some way.
Just out of curiosity, could you check out what is the value in your environment for this setting at the instance level?
Never mind, I made a test a couple of hours ago and the two settings are not (or no longer) related to each other, setting the idle time in the apex admin workspace doesn't affect the idle time at the application level.
I remember time ago having issues with the emails too, but at some point I started receiving them again.