Nightly, there is a possible Maintenance Window between 9pm and 10pm Pacific Time. When needed, the maintenance window is expected to be less than 1 hour. If you are logged in at the start time, you should get a system warning at least 10 minutes prior to the system being taken down.
While it is possible, this will not likely occur each night. Though, it may occur on back-to-back nights.
You can continue to try to connect throughout the window, but may be met with errors related to inability to connect to remote servers.