I opened my mattress, and most people recommend letting it sit for 24 hours before sleeping on it, but my fiancé and I went out for dinner for a couple of hours, and it was ready to do! It fit my bed frame perfectly (I bought this in twin) and I slept comfortably like I haven't in a long time. This mattress does not have any sink potential, so if you like mattresses that suck you in, or arch as you lay down, this is not one of them. What I just described is NOT to be confused with hard. 
I give the mattress 4 stars, because I don't believe anything is perfect.