How does the Airport Access Control work?
First of all, I would suggest setting this up with the Time Capsule first (unplug the AirPort Express). Then, once you have it working on the Time Capsule, you can duplicate it with the AirPort Express.

Option 1

If you want to lock things down as much as possible, then "No Access" should be the default:



And then create a new entry for the cell phone for when you do want to allow access:



However, that will mean that you have to create entries for all of your other devices as well.

Option 2

So your alternative is to make the default "Everyone is welcome":



But then specify when the cell phone is allowed to access:



Which to try?

I would use Option 1 unless you have so many other devices connecting that it would be impractical. 

Option 2 seems like it would be easier to setup, but I have to admit I have not tried it myself.

Time Zone

Time Zone information is set here:



Note that I am still using AirPort Utility 5.6.1 because I find it a lot easier to use than AirPort Utility 6.

You can use 5.6.1 on Mountain Lion, despite what the installer will tell you.

See http://www.tuaw.com/2013/01/22/use-automator-to-get-the-airport-utility-5-6-1-working-on-os-x-1/ and http://www.macworld.com/article/1167965/mountain_lion_and_the_ancient_airport_base_station.html for details on how to install it.