http://goindia.about.com/od/populartrainroutes/qt/delhi-agra-trains.htm
Per that link it seems like I just have two options. Catch a train that leaves at 6:15am or catch one that leaves at 7:10am. What if I want to leave at, say, 10am, instead? Are there trains that run like once every 15 minutes or so?
And once I'm at Agra Cantt what's the best way to get to the Taj Mahal? According to Google Maps the Taj Mahal is about 4mi away from Agra Cantt. That's a walkable distance but in lieu of knowing how much walking I'd want to do at the Taj Mahal I think I'd prefer to conserve my energy. Maybe taxis loiter around at Agra Cantt for passengers as they do at airports? And if they loiter around there do they also loiter around at the Taj Mahal?