1. A system comprising: a processor of a machine; a downtime request module configured to receive attributes of a downtime request for a computer network system, the downtime request module implemented using the processor of the machine, the downtime request identifying a downtime activity to be performed during a downtime and a risk attribute of bringing the computer network system back to an operating condition after the downtime activity is performed during the downtime, wherein the risk attribute depends on a severity of the downtime activity; a user activity computation engine configured to determine user activities of the computer network system based on geographic regions and local times of users accessing the computer network system; and a downtime computation engine configured to calculate a recommended downtime of the computer network system based on the attributes of the downtime request, user activities on the computer network system, the risk attribute, and a criticality of the downtime activity from the downtime request.