About the name
I don't know if the route I describe as "Filo una hora" has a proper name or not. As far as I know it does not. I have called it such because due to the story behind our arrival at the trailhead.
In Machachi we were seeking out camionetas to take us over to the trailhead for Corazón. Some drivers claimed to be able to take us higher, significantly higher, than La Estacion for the standard route. That sounded good to some of the group.
One driver in particular insisted he could get us to within one hour of the summit. I did not believe that for a second but he was so insistant that I figured he must be able to cut a couple - few hours off the hike.
In the end we found ourselves arguing with him at the trailhead. We were about 300 meters / 1000 feet higher than the standard trailhead but without a real trail and clearly much farther away than 1 hour. Maybe fat pickup truck owners can do a cumulative 1,717 m / 5,666 ft in an hour but not us. 5 hours 20 minutes later two of us three made it to the summit. It was the longest 'hour' of our lives.
This route parallels the standard route but starts north of La Estación and about 300 meters / 1000 feet higher. It is not really a trailhead but a road that just stops at a fence. It is north of the large tract of pines visible on the slope and at about the same level. Ask drivers in Machachi to take you a little higher than La Estación and you should get to this vicinity. The exact location is not that important.
Simply take the most convenient path through the grass and along fields up the lower slopes. As you ascend you will encounter other small trails that may make the hiking easier. The higher you go the better the trails become and you will bear to the left and cross a ravine (on trail). Continue steeply upwards at times crossing an old road.
Until now the crater rim and summit have not been visible. Eventually you crest the steep slopes and find yourself on a grassy ridge above a number of abandoned roads. The summit is to the left across an expansive and contoured basin.
One road before you runs left to right ascending a ridge as it turns back to the summit. Continue to this road and follow it up. As you approach the crater rim the road gradually ends, but there is either a very old and overgrown road or an overgrown aqueduct that makes a direct line for the obvious saddle ahead. Continue along it to the saddle.
Here this route meets the standard route as well as the northern route. Turn left and generally follow the left side of the rim to the summit. There are numerous braided trails and occasional cairns leading up.
The route at this point is class 2 with occasional class 3. No exposure.
The summit is long. The first flat spot is not actually the highpoint. Walk further along the narrow ridge.
Day hiking gear is all that is necessary.