Stop using an app during work hours I need to avoid using a personal messaging application in my android phone during work time. 
One way is to uninstall the app before work starts, and install again after the work time. 
Or use some app blockers ? 
Or... what else ?
Depends on your Android version. But go to Settings -->Apps--> Choose App-->Notifications-->And then chose option like Calls, Messages and so on.
I think that this is better than app blocker, becaose most app blockers will completly block apps and messages and this methond will only give you no notification and it takes 15 seconds.