In Classic, 1-60 takes approximately 150-190 hours. With the TBC Prepatch, the experience required for 1-60 goes down by around 30%. In addition, quest experience is nearly doubled. This causes the 1-60 journey to be about 40% shorter depending on how you approach leveling. The new 1-60 time is around 110 - 115 hours.
Now the TBC 60-70 leveling is actually pretty long. Longer than most people remember it. I have done it twice recently on those servers we’re not supposed to talk about so it’s pretty fresh for me. I averaged between 6 and 7 hours per level but I move very quickly, know all the quests, and have frequent dungeon groups. I would say that your average player is looking at least at 60 hours for 60-70.
From 1 - 70 I’d estimate 180 hours conservatively. Or, around 8 days /played (5.5 days for 1-60 and another 2.5 days for 60-70). Obviously, world record holders can do it WAY faster. You’re going to see people hit 70 literally by the second day.