Comment by peteey

Crystal errors tend to be around 20 ppm (parts per million)

After a week, 20 ppm would drift 12 * 10^-6 * 7 * 24 * 60 *60 = 12 seconds.

Your motherboard probably has a cr2032 keeping it powered when unplugged.

Crystals: https://www.digikey.com/en/products/filter/crystals/171?s=N4...