How long does a spinal block last for?

So I had ACL reconstruction surgery today, I was under general anesthesia, and during that they performed a spinal block on my entire left leg. I guess the needle went in right above my groin, I don't know for sure because I was knocked out by then and there is just this random dressing above my groin, so thats what I suppose it it. Well, the question is, how long do there blocks normally last for?