Timed Access not limiting access

3. Yes, everything has their clocks set correctly (does an Airport have its own clock?)

Every AirPort Base Station has their own clock if that is what you are asking. Open AirPort Utility - click Manual Setup. Then click the Base Station tab below the icons. Time settings are here. If you have a Time Capsule, then it would be the Time Capsule tab.

I keep (default) open all the time (Everyday, All Day)

If the default rule is Unlimited Access....then it would seem to be logical to conclude that access is not limited. Therefore, any device with the wireless network password will be able to connect at any (unlimited) time they choose. Are you saying that Unlimited Access should limit access?

If I change the default to No Access, then it works, but I am then required to enter every single WiFi device.

That would be correct. In this setting, you are telling the AirPort that you do not want to allow any devices to connect.....except for those listed with their allowed times. Sorry, I do not know of any shortcuts or workarounds in this regard.

What if I set up the kids on Guest, and limit access just on that network, but keep my main network unlimited access?

I don't see any settings that would allow you set limits on one network, but not on the other.

I have not used the Guest Network feature, but I would expect that the settings under Timed Access are global....applying to both the "main" and "guest" networks equally.

I will play around with the Guest Network over the weekend and report back.

Perhaps another user who has done this will respond as well.

I spent a few minutes with this to check on things.

It does appear that you will need to enter the MAC info in for any "guests" that you want to be able to connect to the Guest Network.

You might want to keep in mind that when you enable the Guest Network, the available bandwidth is split between the "main" and "guest" networks. That being the case, you might want to only enable the Guest Network when you really have "guests".