I wear them until they're ratty and falling apart. And even then, I'll give them one last chance just in case they're still workable XD
I think I've used my current pair of Ardell #110s like, 7-8x now, and they're still perfectly functional, nay, dare I say, in good shape. I don't use mascara on my top lashes after applying them, and I don't even take that good care of them (I've been known to wrap them in a piece of paper and shove it in my bag because I can't find the box). Sturdy little things.