You’ll have to activate the Do not disturb mode. In this way, you will not receive messages notifications but you will still be able to see if there are any unread messages on the envelop icon on the upper right-handed side of the Watch Home Screen. 

To activate the Do not disturb mode:

1. Log into the App and go in the Device page. 
2. Scroll down until you reach “Do not disturb”. Click on it.
3. To turn it on or off, just click on the switch next to “Do not disturb”. If on, you’ll see the “Time period Setting” right below. Click on the numeric times lot on the right to choose the time range you do not want to receive notifications.