Doing it with a file under your control is a very good advise. I ran into a situation where I struggled to be faster in logging in and manually deactivating the watchdog than it rebooted my RasPi
You can update the timestamp of your test file with the touch command.
My setup for the change parameter is 1000 as that results in a wait period that should be long enough if something goes wrong (see above) but still short enough to ensure a “fast” reaction in case of a hangup. But that is a personal decision, everyone needs to experiment a bit to find a personal “correct” setting.
One suggestion from my experience: if you shut down your OH installation for whatever reason, you should keep in mind that the watchdog still looks at the file you’ve configured. And eventually it WILL reboot your machine. That might happen unexpectedly to you and will be done at the most inconvinient point in time according to Murphys Law I did write a command script that shuts down the watchdog before shutting down OH. And a start script with starting OH first and then starting the watchdog:
sudo systemctl start openhab2
sudo systemctl start watchdog