All I can remember is a young boy enters a science lab and finds a time machine with a capsule, and travels threw time and end up in the past in a forest, stumbles across an old man and the old man looks at the control panel and sees what looks to me a car odometer but it is slowly going backwards like a count down. It's been programmed to return automatically. I think the boy goes on and adventure or something and barley makes it back in time when the time capsule returns to the base part in it's own time. The movie was made in the 70's or early 80's I do believe. Does this ring a bell with anyone else.