Go to the settings tab. In the "Update roll out" section, in the right-hand drop-down menu, you can select how frequently you wish to install updates. The choices are: daily, delay 14 days or delay 31 days. After enabling automatic updates by moving the slider to the right, you can also choose the time of day when you want the updates to be installed on the system.
Note that when "All sites" is selected, the Settings tab will not show any settings. To see valid settings, first select a site.