We started the hike around noon and our group of six was able to finish by 3:30pm. There is a very gradual incline the whole time, with the steepest and toughest part being at the beginning.
The hike ends at the El Mirado glacier, but features a lagoon and several beautiful springs along the way. The glacier itself was a little underwhelming, but we did arrive at the end of summer and the sights along the way there more than made up for it.
The sun is very bright here, so I definitely recommend shades and sunscreen, it's also very dry, so bring lots of water. Most of the other hikers we saw were fully outfitted with walking sticks and huge packs, but our group just had some bananas and a couple of liters of water. Despite this we managed to survive the grueling (not really) hike, so don't worry about trying to bring too much.
The town at the base of the hike features little weekend cabins as well as a couple of small groceries, so you aren't completely isolated when you reach this small offshoot of the Maipo Valley.
It's a truly stunning area, we were there as the leaves were beginning to change. It was quite cool at night, but the temperatures during the day were comfortable enough to wear T-shirts in. If you can stay here overnight the stargazing is unbelievable, I'm not sure what the lodging situation is like, we rented one of the small cabins at the base of the hike through word of mouth. There are also some largish towns within half hour drive that definitely have hotel/hostel space.
I would recommend this hike to anyone who can get here, it's a stunning area with completely breathtaking scenery both on the drive there and in the valley itself.