doesn't usually affect digital quartz watches, but it can affect
analogue watches, which use a tiny electric motor to turn the hands.
Powerful magnetism can affect the performance of this motor.
The good news is that although analogue watches may gain time, lose time, or even stop under the influence of powerful magnetic fields, they will usually return to normal time-keeping as soon as they leave the source of magnetism. (You may need to reset your watch, of course.)
Avoid putting your watch near medical equipment, headphones, loudspeakers, or refrigerator door magnets. Electric mixers and blenders and a wide range of other electrical equipment may also have strong enough magnetism to affect timekeeping.