IBKR operates four main computing centers around the globe; two in the U.S, one in Europe and one in Hong Kong. New customers are automatically assigned to one of these server facilities based upon their location and/or trading preferences.
Trading is available 24 hours a day, 7 days a week with the exception of system reset times described in the System Availability table on IBKR website.
The reset period describes the duration during which your account may be unavailable for a few seconds. It does not indicate that the entire system will be unavailable for the full reset period. During a reset period, there may be an interruption in the ability to log in or manage orders. Existing orders (native types) will operate normally although execution reports and simulated orders will be delayed until the reset is complete.
During the Friday evening reset period, all services will be unavailable in all regions for the duration of the reset.
See also How to check and solve connectivity issues affecting the Trader Workstation (TWS) in IBKR KB.
For further information on system availability, please contact IBKR Technical Assistance Center via Message Center ticket.