Would N50 or N40 magnets safe to use?

I'd go with N40, N50 seems like it could be too strong.

Thanks...is there a time limit as to how long they should be worn and how many times a day they should be worn? I've been looking, and I've seen people have posted that it is best to wear them for a short time off and on throughout the day versus being worn overnight, though I'd rather just wear them over night.