There is such a thing as too few features.
Apple stripped a lot out of Airport Utility between v5 and various v6 iterations. Among other things they made it much harder to find the MAC address for a connected device. You need this address to control access times.
The trick is to Option-double-click the base station to get the Summary tab, from which you can see the MAC address. You can’t copy paste that address however. To do that run the terminal command [arp -a]. Look up the IP and MAC address, that you can copy paste.
Of course you may find copy-paste isn’t all that useful. I tried a copy-paste operation into the MAC address field of Airport Utility 6.3.2 and the “Save” button stayed unclickable. I had to type the MAC address in character by character to enable the Save button.