When an ESXi transport node's connected controller goes down, it takes about 5 minutes for the transport node to connect to another controller.
An ESXi transport node is normally connected to a specific controller in a controller cluster. You can find the connected controller with the CLI command get controllers. If the connected controller goes down, it takes about 5 minutes for the transport node to be connected to another controller.
The transport node attempts to re-connect to the controller that is down for a certain amount of time before giving up and connecting to another controller. The whole process takes about 5 minutes. This is expected behavior.