In October 2017, I made a long day trip from Santiago to Sewell Mining Town. Weekend trips organized by VTS (http://www.vts.cl) depart at 8:30 am from the international coffee chain just outside Baquedano metro station, one of the major transfer stations, and return to the same location around 7:30 pm, nearly 11 hours later.

If you take the trip on a Sunday, as I did, bear in mind that the tour does not stop for lunch (included) until after the visit, around 4:30pm, and that most local stores in Santiago don't open on Sundays until after the departure time, so you won't be able to purchase breakfast or snacks until the first stop, more than an hour after departure, outside a supermarket in Rancagua, where other visitors join the tour.