See Example Custom List Widgets. You only need to define the widget once then apply it to your six thermostats. You could event use the Humidifier Setpoint as a template.
You have two options here.
With Autoupdate set on, which is the default, a little autoupdate service will receive the command and predict what the Item’s new state will be once the device processes the command and updates the Item accordingly. This results in immediate feedback in the UI that your command was sent but it means that if your device takes some time to process the command the Item will not reflect the true state of the thermostat.
With Autoupdate set to off, which can be done in Item metadata, the Item will not change state until the device reports back that it’s changed state. This can take some time for some devices, some never report back at all, and the Item’s state and UI will not change until the thermostat actually changed in response to the command.
Those are your choices. Most of the time one will output the state of the Item as part of the widget so it might work to turn off Autoupdate and you can watch that output to see when the thermostat changed.
But if these are zwave thermostats they should be changing in less than a second anyway so I don’t know that you’d notice much of a difference (unless they are battery powered in which case it could be hours). If they take longer then that something is wrong with your mesh network.