If this is with respect to UCS, switchover between the primary and secondary UCS 6120 will result in a control plane outage. The time for the control plane to recover is a funtion of the size of the managed environment. It will take longer with more managed devices.
Control plane failover affects the ability to perform active management of the UCS. It does not affect the data plane.
Unless, there is an actual switch reload or total failure. Then the data plane switch over can take several seconds. Impact to hosts will depend on whether A-B, B-A HA is configured, or the NIC teaming, or, if SAN dual fabric with multipathing is configured.
In short, there are no commands available to decrease the UCS managment recovery time.