Who knows?

But if your watch fails a week after you expose it, will you blame the
magnet?

Would it have failed anyway? Was it coincidence?

If the watch has value to you - monetarily, sentimental or otherwise -
take it off when you do things that you aren't sure of the damage that
might be done to it.

I mean, you wouldn't wear it when swimming, right?

Now, on the other hand, if you just want to know - lay the ******* on
the magnet for a week and see if it still works.