How long will your springs last? How long is a piece of string? It isn't a question that can just be answered like that. It depends on a whole variety of other things. Are your springs fibreglass or carbon, how often do you go out on them? How long for each time? How hard do you use them? Just for the occasional bounce around or serious stunt jumping?
Mine broke a couple weeks ago and I got mine in January. However, mine had a slight crack in one spring when I got them so I'm not the best example to match your springs against.