how do i lengthen the time before an app times out?

I use many different game apps on my Acer tablet. My problem is that some of these apps require me to sit and simply watch as a troop marches (game of war). This will occasionally time out the device and will go back to the main screen after closing the app for innactivity. I was told I have to change the time on my tablet and it is not an in game setting. Any help would be greatly appreciated. Thank you.