There is no way to do it with SmartThings itself, but there are devices made for exactly this purpose. There are several discussion threads in the forum about them. See:
In particular, 3GStore, EZOutlet, and ResetPlug all make devices for this purpose, with different features.
Ankuoo also offers a very inexpensive stripped down version for under $20. No notifications, only one outlet, but it does have both pings and a once a day timer option.