The default timeout for SSH on NSX-T Manager is 10 minutes (600 seconds). This is rather annoying when you need to make a cup of tea and come back and all your sessions have disappeared.
To remove the SSH timeout connect to the NSX Manager via the admin account using SSH.
nsx01> set cli-timeout 0
You can set it to the value (in seconds) of your choice if you prefer to keep some form of timeout