I have two teenagers, and I sometimes need to control their internet usage. For example, teen 1 might be limited to using the internet for two hours in the afternoon and one in the evening. Teen 2 might have unlimited access to the internet until 10 pm, and then none until eight the next morning. Of course my own access should continue uninterrupted. Is there a way to do this with their devices – Macs as well as iOS devices?
Vance Makin

The Parental Controls system preference may seem like the perfect fallback for the Mac, but in your case it’s not. Parental Controls limits access to the Mac entirely rather than simply limiting internet access. For the internet, your fallback plan is your router. Most routers allow you to limit access based on a device’s MAC address. It works this way on an AirPort Extreme base station:

Launch AirPort Utility, select your router, and click the Manual Setup button. Select the AirPort tab at the top of the window and click the Access Control tab. From the MAC Address Access Control pop-up menu, choose Timed Access. This is where you begin setting up limits.

Click the plus-sign (+) button at the bottom of the pane, and in the sheet that appears enter the MAC address for the devices you want to limit. On an iOS device, you’ll find this address by choosing Settings > General > About and locating the Wi-Fi Address Entry. On a Mac, hold down the Option key and select System Profiler (Snow Leopard) or System Information (Lion) from the Apple menu. When System Profiler appears, select Network and then, in the Active Services column to the right, select AirPort. Search for the MAC Address entry in the results below.

Once you’ve entered the MAC Address, give it a description (‘Billy’s iPhone,’ for example). Now configure the pop-up menus below. Here you can choose time limits that include No Access, Mondays, Tuesdays, Wednesdays, Thursdays, Fridays, Saturdays, Sundays, Weekdays, and Weekends. Click the plus-sign button in this sheet, and you can add more entries – you can, for example, include two entries for each weekday. Click Done when you’re finished, and click the Update button to do just that. The router will block access except during the hours allowed.