It's really different for everyone, depending on how much you can swallow, can be a day, a couple of days, even if they do get you to hospital it's a real battle to stop the damage. I can assure you though if your at home painkillers are enough to stop the pain and if your in hospital and they can't save you they won't let you suffer, is my experience anyway. The actual drinking and first couple of hours are not painful at all. And you do fall into a unconscious state quickly at first, you may wake up again or not at all, you may have to deal with the experience taking longer than other methods, but I think it gets a bad rep on the pain/suffering side of things. And it's easily available so you don't have to plan and pay loads either. It does take longer than other methods but if you decide to ride that bus, then it's something I wouldn't discount.