I am going to assume you mean the screen time out? You may have an app on the tablet that is resetting it. Happens a lot. You may want to check the settings within each app to make sure none of them are set to change the amount of time the screen is on before timing out.
Next I would try making sure the tablet itself, as well as all apps, are updated. Once all updates are done, shut the tablet down and then turn it back on. (totally power it off) and then set the display's time out to 1 minute.
If the problem happens again, you may want to try starting up the device in "Safe Mode" and see if the change happens when in that. If it doesn't, then you have something on the tablet that is interfering that will need to be removed. If it does happen, then you may want to "Hard Reset" the tablet. But save that for last as it will require you back up all your stuff from the tablet to another device as it wipes the tablet.