Apparently the new hole has to be 28 inches or 70cm in diameter. This is about 4.5 times the width of the holes already drilled, or 20 times the cross-sectional area. It sounds like you'll know better than I do what torque would be required to drill this. One of the physicists here can do the maths.

The other variable is the rock type, of course. I don't know what they're drilling through but rock hardness can vary enormously.

I've read that they have to drill the hole quite a way from where the miners are and that the miners themselves will have to excavate a substantial amount of material to reach the rescue shaft. I suppose the logistics of bringing 250+ cubic metres of rock to the surface are not negligible.If they can't use the existing boreholes, they can't benefit from the work already completed either.

there is considerable debate among local mining engineers as to exactly how long the drilling will take, with many suggesting that it will be done in a much quicker time than the 3 to 4 months suggested by the Chilean Government, the longer time allows for the drill to be regularly withdrawn so the walls can be sheathed in metal to prevent collapse, a requirement that many engineers say will not be needed due to the strength of the rock being drilled through, also there is a time allowance built in for breakdowns, clearance by the miners of rock falling down the pilot shaft and the like.

In all likelihood the miners will be reached in far less time than the worse case scenarios, with the drillers becoming heroes. If they published the earliest possible time they would be reached and then arrived a couple of weeks later they would be villains. Unfortunately there appears to be more spin than just drill torque involved in predicting the amount of time it will take to reach the miners.