If you’re using it on a modern flat screen, put it in game mode and you should be fine.
Warning: composite and S-video look like shit on modern TVs. The reason most people mention input lag is because many run older consoles through an upscaler that outputs HDMI such as this or this. This is where input lag can sometimes become and issue.
Honestly, for your situation, you are best off using your modded console on a tube TV that has an S-Video input. I really don’t see the value in upscaling Atari graphics to HD.