I'm looking to find an old science fiction story that I read in an anthology many years ago (probably in the 60s) called 'What Time Is It?' It's about a group of high-school or college age boys that hop into their professor's time machine and wind up in the past fighting Indians and then hop into the future where all the cars are tear-drop shape. The story is very simple-reading but I've not found it anywhere since. Ideas, anyone?