/3/ - 3DCG

>>956147
It's in the render options. Not preferences.
Right hand side of the main screen, the little button that looks like a camera
Set render engine to cycles and device to GPU compute as in the image

Below that you'll see time limit which lets you set in seconds how long it'll take on each frame.
0.2 seconds is enough for most purposes but if you have a large scene or are doing animations you can set it higher to 1 or 2 seconds.