It depends on if you stay in range or not, I don't know what the range is off the top of my head but I think it's increased by your skill.
It takes 12 seconds to wear off but you have to be out of range for the full 12 seconds for it to stop. If you come back in range on 11 seconds it won't wear off.
Being hidden/invised also counts as being out of range however this isn't the same thing as maintaining line of sight. You can not have line of sight and it will stay discorded.
It can't be resisted but it can fail like any other skill attempt. Based on your bards skills and the targets barding difficulty and the type/quality of the instrument you use. If you are below the minimum requirements it won't even let you try.