Most raids take about an hour or 2, depending on your groups competency level. If you're a team of 6 with little experience, they can most certainly take much longer. Life will be much easier if you can find at least 1 person who knows what's going on to guide the team. Last Wish is on the longer side of D2s raids and does ask for a bit more teamwork than others do so if that's where you want to start, I'd very much recommend finding someone experienced to help. Do yourself and your future team a favor and watch a guide on YT (you don't need to memorize it) so you are familiar with what lies ahead. Some familiarity can save everyone a lot of time and frustration. Raids are some of D2s best content and are fun with the right people. If you do come across a bad group, don't write off raiding right away, and keep searching.